托福TPO30阅读Passage2原文文本+题目+答案解析
为了帮助大家高效备考托福，为大家带来托福TPO30阅读Passage2原文文本+题目+答案解析，希望对大家备考有所帮助。
The Pace of Evolutionary Change A heated debate has enlivened recent studiesof evolution.Darwin's original thesis,and theviewpoint supported by evolutionary gradualists,isthat species change continuously but slowly and insmall increments.Such changes are all but invisible over the short time scale of modernobservations,and,it is argued,they are usually obscured by innumerable gaps in theimperfect fossil record.Gradualism,with its stress on the slow pace of change,is a comfortingposition,repeated over and over again in generations of textbooks.By the early twentiethcentury,the question about the rate of evolution had been answered in favor of gradualism tomost biologists'satisfaction. 最近的一个关于进化的研究引发了激烈的争论。
达尔文的原始论点和进化渐进主义者支持的观点是物种会持续地改变，但非常缓慢，增量也很小。
这种改变是普遍的，但是现在短时间的观察是不能察觉的，并且，这个观点声称，它们通常被掩盖于不完美的化石记录的不可计数的缺失中。
渐进主义及其对物种缓慢变化的引力让人欣然接受，并在世代的教科书中重复出现。
在20世纪早前之前，令大部分的生物学家满足于利用渐进主义来回答关于进化速率的问题。
Sometimes a closed question must be reopened as new evidence or new arguments basedon old evidence come to light.In 1972 paleontologist Stephen Jay Gould and Niles Eldredgechallenged conventional wisdom with an opposing viewpoint,the punctuated equilibriumhypothesis,which posits that species give rise to new species in relatively sudden bursts,without a lengthy transition period.These episodes of rapid evolution are separated byrelatively long static spans during which a species may hardly change at all. 有时，已经有了结论的问题必须由在已有证据基础上出现的新的证据和新的论点使其重新展开讨论。
在1972年，古生物学者Stephen Jay Gould和Niles Eldredge用相反的论点挑战了世俗的结论，即断点平衡说，它假设了物种演变为新的物种是通过相对突然的爆发，并非通过长时间的过渡时期。
迅速的进化期被时间相对更长的静态期分开，而在静态时期，物种是几乎完全不变的。
The punctuated equilibrium hypothesis attempts to explain a curious feature of thefossil record—one that has been familiar to paleontologist for more than a century but hasusually been ignored.Many species appear to remain unchanged in the fossil record for millionsof years—a situation that seems to be at odds with Darwin's model of continuous change.Intermediated fossil forms,predicted by gradualism,are typically lacking.In most localities agiven species of clam or coral persists essentially unchanged throughout a thick formationof rock,only to be replaced suddenly by a new and different species. 断点平衡论试着去解释化石记录的一个古怪的特点----在超过一个世纪的时间里它已经为古生物学者所熟悉，但一直被忽视。
许多物种似乎在上百万年的化石记录中一直没有改变，这个情况与达尔文的模型所支持的物种的持续变化相悖。
进化渐进论的支持者所预测的中间状态的化石一直没有出现。
在大部分蛤和珊瑚的聚集地，其化石在很厚的岩石中都实际上没有变化，只是突然被另一新的并且不同的物种而取代。
The evolution of North American horse,which was once presented as a classic textbookexample of gradual evolution,is now providing equally compelling evidence for punctuatedequilibrium.A convincing 50-million-year sequence of modern horse ancestors—eachslightly larger,with more complex teeth,a longer face,and a more prominent central toe—seemed to provide strong support for Darwin's contention that species evolve gradually.But close examination of those fossil deposits now reveals a somewhat different story.Horsesevolved in discrete steps,each of which persisted almost unchanged for millions of years andwas eventually replaced by a distinctive newer model.The four-toed Eohippus preceded thethree-toed Miohippus,for example,but North American fossil evidence suggests a jerky,uneven transition between the two.If evolution had been a continuous,gradual process,one might expect that almost every fossil specimen would be slightly different from every year. 北美马的进化曾经被用作经典的教科书案例来证明渐变进化论，现在却为断点平衡学提供了同样有说服力的证据。
一个有说服力的5千万年的马祖先的进化模型----每一代都稍稍大一点，有更复杂的牙齿，更长的脸，和中间更突出的脚趾----这一切都看似强有力的支持了达尔文的论点，物种是逐步地进化的。
但是，对这些化石更严谨的验证现在揭示了一个不太一样的故事。
马是在不连续的步骤中进化的，其中每个进化步骤中间都有上百万年时间保持不变，在最后被一个不同的更新的模型取代。
比如四只脚趾的Eohippus在三只脚趾的moihippus之前，但北美化石证据表明在这之间有一个不平稳的，不均衡的转换过程。
如果进化一直都是连续，渐进的过程，人们应该预期到的是每年的化石样本都会存在细微的差别。
If it seems difficult to conceive how major changes could occur rapidly,consider this:analteration of a single gene in files is enough to turn a normal fly with a single pair of wings intoone that has two pairs of wings. 如果很难设想大的改变会迅速发生，想想这些：一个单一基因的改变就足以将有一对翅膀的苍蝇变成两对翅膀。
The question about the rate of evolution must now be turned around:does evolutionever proceed gradually,or does it always occur in short bursts?Detailed field studies of thickrock formations containing fossils provide the best potential tests of the competing theories. 关于进化速度的问题现在发生了转变：进化过程是逐渐发生的么，还是总是突然短时间的爆发?对含有化石的厚岩层的细致的现场调查可以检验这两个备受争论的理论。
Occasionally,a sequence of fossil-rich layers of rock permits a comprehensive。
托福TPO30阅读Passage2原文文本+题目+答案解析
托福TPO30阅读Passage2原文文本+题目+答案解析为了帮助大家高效备考托福，为大家带来托福TPO30阅读Passage2原文文本+题目+答案解析，希望对大家备考有所帮助。
The Pace of Evolutionary ChangeA heated debate has enlivened recent studiesof evolution.Darwin's original thesis,and theviewpoint supported by evolutionary gradualists,isthat species change continuously but slowly and insmall increments.Such changes are all but invisible over the short time scale of modernobservations,and,it is argued,they are usually obscured by innumerable gaps in theimperfect fossil record.Gradualism,with its stress on the slow pace of change,is a comfortingposition,repeated over and over again in generations of textbooks.By the early twentiethcentury,the question about the rate of evolution had been answered in favor of gradualism tomost biologists'satisfaction.最近的一个关于进化的研究引发了激烈的争论。
达尔文的原始论点和进化渐进主义者支持的观点是物种会持续地改变，但非常缓慢，增量也很小。
托福TPO30听力Conversation2文本+题目+答案解析
为了帮助大家高效备考托福，为大家带来托福TPO30听力Conversation2文本+题目+答案解析，希望对大家备考有所帮助。
托福TPO30听力Conversation2文本 Narrator: Listen to a conversation between a student and his art history professor. Professor: How was the museum? Student: Great. I hadn’t been there for a few years. Professor: Did you enjoy the Van Gogh painting? Student: That’s the thing. Looks like I have to change my topic. Professor: Hmm… we are getting close to the deadline. You were writing about the theme of night in the paintings of Vincent Van Gogh. It’s a wonderful topic. Student: I know. People don’t usually think of Van Gogh as an artist of nocturnal themes. They think of brightness, sunshine, all that yellow and orange. Professor: You are right of course about the intense light associated with his daytime paintings. But his night paintings don’t exactly lack brightness. Student: That’s the paradox that I really like, the paradox of painting a nighttime scene using so much color and light. So I was planning to focus mostly on his painting Starry Night. Professor: But? [Student: When I went to the museum to look at the actual painting, like you told me to. It wasn’t there. Professor: Really? Isn’t it part of the permanent collection? Student: Yes. But it’s on loan right now to a museum in Europe. Professor: Ah, I see. Well, I am strict about having students write about paintings they can observe firsthand. Student: Well, I found another painting I could study instead. Professor: OK. Student: I read that there are two paintings called Starry Night.The first one was done by the French realist painter Millet.It may have been the inspiration for Van Gogh’s painting. Millet’s painting is located near my family’s house in Connecticut.And I am going there this weekend and could study it then. I made sure it’s not out on loan. Professor: That definitely would work then. Van Gogh copied many of Millet’s compositions. We know that he really admired Millet’s work. And a lot of us think Van Gogh saw this particular painting by Millet in Paris in the late 1700s. Student: Yeah. Although Millet was a realist painter, and Van Gogh a post-impressionist, the two paintings still share lots of features, not just the name. The most striking shared feature has got to be the amazing light effects. I am excited to go see it. But one other thing … Professor: Uh-huh. Student: I was thinking about getting a head start on my next assignment while I am at the gallery in Connecticut, the assignment on miniatures. They have a lot of miniature portraits of children as part of their permanent collection. Professor: American miniatures? Student: Yeah. So I figured I could also get started on that essay, study a few while I am there. I’d focus on the meaning of the objects that some of the children are holding, some are holding flowers, one child has a rattle, another a toy violin… Professor: That would be fine. Uh, those objects…we call them attributes. The attributes chosen to be included in a particular miniature was often meant to communicate parents’ hopes and dreams for their child. So I think you’ll learn a lot about how people viewed children at the time the miniature paintings were done. 托福TPO30听力Conversation2题目 1.What are the speakers mainly discussing? A. The student's idea about his class assignments. B. The influence of one painter on another. C. The student's recent visit to museum in Connecticut. D. The challenges associated with painting at night.。
托福TPO29阅读Passage2原文文本+题目+答案解析
为了帮助大家高效备考托福，为大家带来托福TPO29阅读Passage2原文文本+题目+答案解析，希望对大家备考有所帮助。
Competition When several individuals of the same species or of several different species depend on the same limited resource,a situation may arise that is referred to as competition.The existence of competition has been long known to naturalists;its effects were described by Darwin in considerable petition among individuals of the same species(intraspecies competition),one of the major mechanisms of natural selection,is the concern of evolutionary petition among the individuals of different species(interspecies competition)is a major concern of ecology.It is one of the factors controlling the size of competing populations,and extreme cases it may lead to the extinction of one of the competing species.This was described by Darwin for indigenous New Zealand species of animals and plants,which died out when competing species from Europe were introduced. 当同一物种的不同个体或不同的物种都依靠同一有限资源时，这种情况往往会引发成所谓的竞争。
托福TPO30听力L2文本
托福TPO30听力L2文本TPO 30 Lecture 2 PaleontologyNarrator Listen to part of a lecture in a paleontology class. Professor As we’ve discussed, birds are apparently descendants of dinosaurs and shared many commonalities with some dinosaur species, like...um...feathers and maybe even flight and of course egg laid. OK. So, many paleontologists, myself included, have wondered about other similarities between dinosaurs and birds. Since adult dinosaur fossils have sometimes been discovered near or on top of nests, we’ve been looking at the dinosaur parenting behavior. Student Parenting behavior, well, that sounds so gentle and caring. But dinosaurs were ferocious reptiles and reptiles don’t take care of their young, do they? Professor Well, some reptiles incubate their eggs, crocodiles do. And as for popular attitudes towards dinosaurs...well, take the Oviraptor for instance. In the 1920s, a paleontologist discovered the fossil remains of a small dinosaur near a nest containing eggs. He assumed the dinosaur was stealing the eggs, so he named it Oviraptor that means egg thief in Latin, which fueled the generally negative public image of such dinosaurs. But by the 1990s, other experts had convincingly made the case that instead of robbing the nest; the Oviraptor was probably taking care of the eggs. You see, dinosaurs’ closest living relatives – birds and crocodiles – display nesting behavior. And dinosaur fossils have been found in postures that we now believe to indicate brooding behavior, that is, sitting on the eggs until they hatch. So we are curious about the type of care dinosaurs gave to their young. And we’d like to figure out which dinosaur parent, the male or the female gave the care. Student Sho uldn’t the behavior ofcrocodiles and birds give us some clues then?Professor Well, with crocodiles, it is the female who guards the nest, and with birds, it depends on the species, it can be the male or the female that takes care the eggs, or both. In over 90 percent of all bird species, both parents take care of the eggs and the young birds. Student But sometimes it’s just the male? Professor Well, exclusive care by the male parent is much less common, but it does occur. Now, for animals other than birds, the care of young by both parents is pretty unusual in the animal kingdom. Males contribute to parental care in fewer than five percent of all mammalian species. It’s even less frequent among reptiles. And exclusive care by the male is very rare. So researchers have wondered about the evolution of male parenting behavior in birds for quite some time. And now there’s research showing that for some of the birds’ dinosaur relatives, it’s likely that the male parent was also in charge of taking care of the eggs. Student How did they figure that out? Professor Well, first they looked at clutch volume, that’s the number of eggs in the nest of crocodiles, birds and three types of dinosaurs, including Oviraptors that are thought to be closely related to the dinosaur ancestors of birds. So when researchers examined fossilized remains of nests, they found that the dinosaurs had larger clutch volumes, more eggs in the nests that is, than most of the crocodiles and birds that were studied. But, and this is important, their clutch volumes matched those of birds that have only male parental care. You see, bird species in which only the males take care of the nest tend to have the largest clutches of eggs. Student So what’s the connection between bird and dinosaur behavior? Professor Well, researchers nowbelieve, because of this study, that the male parenting behavior of these birds might have its origins in the behavior of dinosaurs.Student Based only on evidence of clutch volume size, the number of eggs? Professor No, there’s more. They also examined the fossilized bones of those three types of dinosaurs that were found on or near nests to determine their sex. You see, adult female birds during egg production produce a layer of spongy bone tissue inside certain long bones. And so did female dinosaurs of the kinds that were investigated. This spongy tissue serves as a source of calcium for eggshell formation. But when the dinosaur fossils were examined, there were no spongy bone deposits. Student Meaning that those dinosaurs on the nests were probably adult males who wouldn’t have needed calcium for making eggshells. Professor Exactly. And then there’s this: birds like the kiwi, the ostrich and the emu; they share certain physical characteristics with these dinosaurs. And interestingly, they also show a consistent pattern of nest care by the male.。
托福TPO31阅读Passage2原文文本+题目+答案解析
为了帮助大家高效备考托福，为大家带来托福TPO31阅读Passage2原文文本+题目+答案解析，希望对大家备考有所帮助。
Early Children Education Preschools—educational programs for children under the age of five—differ significantly from one country to another according to the views that different societies hold regarding the purpose of early childhood education.For instance,in a cross-country comparison of preschools in China,Japan,and the United States,researchers found that parents in the three countries view the purpose of preschools very differently.Whereas parents in China tend to see preschools primarily as a way of giving children a good start academically,Japanese parents view them primarily as a way of giving children the opportunity to be members of a group.In the United States,in comparison,parents regard the primary purpose of preschools as making children more independent and self-reliant,although obtaining a good academic start and having group experience are also important. 由于不同社会持有的关于儿童早教目的观点的不同，学前班(5岁以下儿童的教育项目)的形式在不同国家也大不相同。
托福TPO33阅读Passage2原文文本+题目+答案解析
为了帮助大家高效备考托福，为大家带来托福TPO33阅读Passage2原文文本+题目+答案解析，希望对大家备考有所帮助。
Railroads and Commercial Agriculture in Nineteenth-Century United States By 1850 the United States possessed roughly 9,000 miles of railroad track;then years later it had over 30,000 miles,more than the rest of the world combined.Much of the new construction during the 1850s occurred west of the Appalachian Mountains–over 2,000 miles in the states of Ohio and Illinois alone. The effect of the new railroad lines rippled outward through the economy.Farmers along the tracks began to specialize in corps that they could market in distant locations.With their profits they purchased manufactured goods that earlier they might have made at home.Before the railroad reached Tennessee,the state produced about 25,000 bushels(or 640 tons)of wheat,which sold for less than 50 cents a bushel.Once the railroad came,farmers in the same counties grew 400,000 bushels(over 10,000 tons)and sold their crop at a dollar a bushel. The new railroad networks shifted the direction of western trade.In 1840 most northwestern grain was shipped south down the Mississippi River to the bustling port of New Orleans.But low water made steamboat travel hazardous in summer,and ice shut down traffic in winter.Products such as lard,tallow,and cheese quickly spoiled if stored in New Orleans’hot and humid warehouses.Increasingly,traffic from the Midwest flowed west to east,over the new rail lines.Chicago became the region’s hub,linking the farms of the upper Midwest to New York and other eastern cities by more than 2,000 miles of track in 1855.Thus while the value of goods shipped by river to New Orleans continued to increase,the South’s overall share of western trade dropped dramatically. A sharp rise in demand for grain abroad also encouraged farmers in the Northeast and Midwest to become more commercially oriented.Wheat,which in 1845 commanded$1.08 a bushel in New York City,fetched$2.46 in 1855;in similar fashion the price of corn nearly doubled.Farmers responded by specializing in cash crops,borrowing to purchase more land,and investing in equipment to increase productivity. As railroad lines fanned out from Chicago,farmers began to acquire open prairie land in Illinois and then Iowa,putting the fertile,deep black soil into production. Commercial agriculture transformed this remarkable treeless environment.To settlers accustomed to eastern woodlands,the thousands of square miles of tall grass were an awesome sight.Indian grass,Canada wild rye,and native big bluestem all grew higher than a person.Because eastern plows could not penetrate the densely tangled roots of prairie grass,the earliest settlers erected farms along the boundary separating the forest from the prairie.In 1837,however,John Deere patented a sharp-cutting steel plow that sliced through the sod without soil sticking to the blade.Cyrus McCormick refined a mechanical reaper that harvested fourteen times more wheat with the same amount of labor.By the 1850s McCormick was selling 1,000 reapers a year and could not keep up with demand,while Deere turned out 10,000 plows annually. The new commercial farming fundamentally altered the Midwestern landscape and the environment.Native Americans had grown corn in the region for years,but never in such large fields as did later settlers who became farmers,whose surpluses were shipped east.Prairie farmers also introduced new crops that were not part of the earlier ecological system,notably wheat,along with fruits and vegetables. Native grasses were replaced by a small number of plants cultivated as commodities.Corn had the best yields,but it was primarily used to feed livestock.Because bread played a key role in the American and European diet,wheat became the major cash crop.Tame grasses replaced native grasses in pastures for making hay. Western farmers altered the landscape by reducing the annual fires that had kept the prairie free from trees.In the absence of these fires,trees reappeared on land not in cultivation and,if undisturbed,eventually formed woodlots.The earlier unbroken landscape gave way to independent farms,each fenced off in a precise checkerboard pattern.It was an artificial ecosystem of animals,woodlots,and crops,whose large,uniform layout made western farms more efficient than the more-irregular farms in the East. 译文：十九世纪美国的铁路和商品农业 在1850年之前美国有约9，000英里铁轨，几年之后铁轨的长度增加到30,000多英里，比世界上其他地方的总和还要多。
托福阅读真题第30篇Zebra_Stripes（答案文章最后）
托福阅读真题第30篇Zebra_Stripes（答案文章最后）Zebras, horse like animals native to the grasslands of frica, are known for their distinctive black and white stripes. Historically many scientists thought zebras' stripes served to camouflage (hide) them from predators, such as lions and hyenas. This assumption was based on the observation that other animals, such as tigers, have similar stripes that make them less visible. However, in recent years scientists have noted that zebras' environment and behavior are not well suited to camouflage by stripes. Tigers often inhabit heavily forested areas in which there, vertical stripes help them blend in with the surrounding trees, but zebras typically inhabit open grasslands. Unlike tigers, who use stealth to stalk their prey, zebras are herbivores that rarely hold still when threatened by predators; instead, they rely on their good eyesight to spot predators at a distance and flee at any signal of danger.zebra's stripes may help to protect it in other ways. Stripes may help zebras blend in with each other, rather than blend in with their environment. Zebras live in large herds, and they flee as a group when threatened. The dense pattern of moving zebra stripes may appear as a mass of confusing images, making it difficult for predators to target individual zebras. atching a fleeing zebra requires a precisely timed final leap, and a zebra's stripes may interfere with predators' perception of distance. ecause zebras have some ability to defend themselves by using their hind legs to kick at pursuing predators, at times powerfully enough to cause serious injury, a zebra's distinctive stripes may also serve as a Warning that encourages predators to seek less dangerous prey. However, none of these explanations is stronglysupported by observation. Zebras are killed by lions about as frequently as other unstriped prey animals.More recently, scientists have suggested that the primary purpose of stripes is to protect zebras from biting flies. The grasslands of frica are home to a number of species of flies that feed on the blood of large mammals and can cause considerable damage through blood loss and the transmission of diseases. Laboratory tests have shown that biting flies are less likely to land on objects covered in black and white stripes than on solid black on white surfaces. It is not yet known why biting flies would avoid striped objects. but scientists have suggested that the explanation lies in the mechanisms of flies' vision, which is simple and apparently confused by stripes. The stripes may make it difficult for flies to detect the outline of a zebra's body or cause the flies to confuse a zebra for a collection of thin, vertical objects that do not resemble potential victims. Scientists have analyzed the stomach contents of wild biting flies and have found relatively little zebra blood.If stripes are an effective means of protection against biting flies. then why have other animals not evolved stripes as well? One theory is that zebras are particularly vulnerable to flies because of their unusually short hair and developed stripes as an alternative protective measure. Horses, which are closely related to zebras, are indeed extremely susceptible to biting flies when imported to frica. They are frequently infected by fly-borne parasitic infections which are often fatal even when veterinary treatment is provided. Horses do not develop immunity to the parasites and so can be repeatedly re-infectedOther puzzles remain. For instance, biting flies seem to be most discouraged by horizontal stripes, but the stripes on zebrasare mostly vertical. More mysteriously, not all zebras are covered in stripes: the quagga, an extinct subspecies of zebra. had fainter stripes that were present only on the front half of its body. If stripes protect from flies, why would the quagga lack protection on half of its body? This cannot be explained by environmental factors. because quaggas' range overlapped with that of fully striped zebras. One possible explanation is that if they only have stripes on half of their body, quaggas can more easily distinguish between. their own and other species of zebra, making it easier for them to follow the solid-colored hindquarters when fleeing from predators. This behavioral hypothesis is unfortunately impossible to test, because scientists can only study the quagga through preserved museum specimens and a handful of nineteenth-century photographs.1.Zebras, horse like animals native to the grasslands of frica, are known for their distinctive black and white stripes. Historically many scientists thought zebras' stripes served to camouflage (hide) them from predators, such as lions and hyenas. This assumption was based on the observation that other animals, such as tigers, have similar stripes that make them less visible. However, in recent years scientists have noted that zebras' environment and behavior are not well suited to camouflage by stripes. Tigers often inhabit heavily forested areas in which there, vertical stripes help them blend in with the surrounding trees, but zebras typically inhabit open grasslands. Unlike tigers, who use stealth to stalk their prey, zebras are herbivores that rarely hold still when threatened by predators; instead, they rely on their good eyesight to spot predators at a distance and flee at any signal of danger.2. zebra's stripes may help to protect it in other ways. Stripeswith their environment. Zebras live in large herds, and they flee as a group when threatened. The dense pattern of moving zebra stripes may appear as a mass of confusing images, making it difficult for predators to target individual zebras. atching a fleeing zebra requires a precisely timed final leap, and a zebra's stripes may interfere with predators' perception of distance. ecause zebras have some ability to defend themselves by using their hind legs to kick at pursuing predators, at times powerfully enough to cause serious injury, a zebra's distinctive stripes may also serve as a Warning that encourages predators to seek less dangerous prey. However, none of these explanations is strongly supported by observation. Zebras are killed by lions about as frequently as other unstriped prey animals.3. zebra's stripes may help to protect it in other ways. Stripes may help zebras blend in with each other, rather than blend in with their environment. Zebras live in large herds, and they flee as a group when threatened. The dense pattern of moving zebra stripes may appear as a mass of confusing images, making it difficult for predators to target individual zebras. atching a fleeing zebra requires a precisely timed final leap, and a zebra's stripes may interfere with predators' perception of distance. ecause zebras have some ability to defend themselves by using their hind legs to kick at pursuing predators, at times powerfully enough to cause serious injury, a zebra's distinctive stripes may also serve as a Warning that encourages predators to seek less dangerous prey. However, none of these explanations is strongly supported by observation. Zebras are killed by lions about as frequently as other unstriped prey animals.4. zebra's stripes may help to protect it in other ways. Stripeswith their environment. Zebras live in large herds, and they flee as a group when threatened. The dense pattern of moving zebra stripes may appear as a mass of confusing images, making it difficult for predators to target individual zebras. atching a fleeing zebra requires a precisely timed final leap, and a zebra's stripes may interfere with predators' perception of distance. ecause zebras have some ability to defend themselves by using their hind legs to kick at pursuing predators, at times powerfully enough to cause serious injury, a zebra's distinctive stripes may also serve as a Warning that encourages predators to seek less dangerous prey. However, none of these explanations is strongly supported by observation. Zebras are killed by lions about as frequently as other unstriped prey animals.5.More recently, scientists have suggested that the primary purpose of stripes is to protect zebras from biting flies. The grasslands of frica are home to a number of species of flies that feed on the blood of large mammals and can cause considerable damage through blood loss and the transmission of diseases. Laboratory tests have shown that biting flies are less likely to land on objects covered in black and white stripes than on solid black on white surfaces. It is not yet known why biting flies would avoid striped objects. but scientists have suggested that the explanation lies in the mechanisms of flies' vision, which is simple and apparently confused by stripes. The stripes may make it difficult for flies to detect the outline of a zebra's body or cause the flies to confuse a zebra for a collection of thin, vertical objects that do not resemble potential victims. Scientists have analyzed the stomach contents of wild biting flies and have found relatively little zebra blood.6.More recently, scientists have suggested that the primary purpose of stripes is to protect zebras from biting flies. The grasslands of frica are home to a number of species of flies that feed on the blood of large mammals and can cause considerable damage through blood loss and the transmission of diseases. Laboratory tests have shown that biting flies are less likely to land on objects covered in black and white stripes than on solid black on white surfaces. It is not yet known why biting flies would avoid striped objects. but scientists have suggested that the explanation lies in the mechanisms of flies' vision, which is simple and apparently confused by stripes. The stripes may make it difficult for flies to detect the outline of a zebra's body or cause the flies to confuse a zebra for a collection of thin, vertical objects that do not resemble potential victims. Scientists have analyzed the stomach contents of wild biting flies and have found relatively little zebra blood.7.If stripes are an effective means of protection against biting flies. then why have other animals not evolved stripes as well? One theory is that zebras are particularly vulnerable to flies because of their unusually short hair and developed stripes as an alternative protective measure. Horses, which are closely related to zebras, are indeed extremely susceptible to biting flies when imported to frica. They are frequently infected by fly-borne parasitic infections which are often fatal even when veterinary treatment is provided. Horses do not develop immunity to the parasites and so can be repeatedly re-infected8.Other puzzles remain. For instance, biting flies seem to be most discouraged by horizontal stripes, but the stripes on zebras are mostly vertical. More mysteriously, not all zebras are covered in stripes: the quagga, an extinct subspecies of zebra. had fainterstripes that were present only on the front half of its body. If stripes protect from flies, why would the quagga lack protection on half of its body? This cannot be explained by environmental factors. because quaggas' range overlapped with that of fully striped zebras. One possible explanation is that if they only have stripes on half of their body, quaggas can more easily distinguish between. their own and other species of zebra, making it easier for them to follow the solid-colored hindquarters when fleeing from predators. This behavioral hypothesis is unfortunately impossible to test, because scientists can only study the quagga through preserved museum specimens and a handful of nineteenth-century photographs.9.Zebras, horse like animals native to the grasslands of frica, are known for their distinctive black and white stripes.⬛Historically many scientists thought zebras' stripes served to camouflage (hide) them from predators, such as lions and hyenas.⬛This assumption was based on the observation that other animals, such as tigers, have similar stripes that make them less visible. However, in recent years scientists have noted that zebras' environment and behavior are not well suited to camouflage by stripes. ⬛Tigers often inhabit heavily forested areas in which there, vertical stripes help them blend in with the surrounding trees, but zebras typically inhabit open grasslands.⬛Unlike tigers, who use stealth to stalk their prey, zebras are herbivores that rarely hold still when threatened by predators; instead, they rely on their good eyesight to spot predators at a distance and flee at any signal of danger.10.。
托福TPO3阅读Passage2原文文本+题目+答案解析
为了帮助大家高效备考托福，为大家带来托福TPO3阅读Passage2原文文本+题目+答案解析，希望对大家备考有所帮助。
▉托福TPO3阅读Passage2原文文本： Depletion of the Ogallala Aquifer The vast grasslands of the High Plains in the central United States were settled by farmers and ranchers in the 1880s. This region has a semiarid climate, and for 50 years after its settlement, it supported a low-intensity agricultural economy of cattle ranching and wheat farming. In the early twentieth century, however, it was discovered that much of the High Plains was underlain by a huge aquifer (a rock layer containing large quantities of groundwater). This aquifer was named the Ogallala aquifer after the Ogallala Sioux Indians, who once inhabited the region. The Ogallala aquifer is a sandstone formation that underlies some 583,000 square kilometers of land extending from northwestern Texas to southern South Dakota. Water from rains and melting snows has been accumulating in the Ogallala for the past 30,000 years. Estimates indicate that the aquifer contains enough water to fill Lake Huron, but unfortunately, under the semiarid climatic conditions that presently exist in the region, rates of addition to the aquifer are minimal, amounting to about half a centimeter a year. The first wells were drilled into the Ogallala during the drought years of the early 1930s. The ensuing rapid expansion of irrigation agriculture, especially from the 1950s onward, transformed the economy of the region. More than 100,000 wells now tap the Ogallala. Modern irrigation devices, each capable of spraying 4. 5 million liters of water a day, have produced a landscape dominated by geometric patterns of circular green islands of crops. Ogallala water has enabled the High Plains region to supply significant amounts of the cotton, sorghum, wheat, and corn grown in the United States. In addition, 40 percent of American grain-fed beef cattle are fattened here. This unprecedented development of a finite groundwater resource with an almost negligible natural recharge rate—that is, virtually no natural water source to replenish the water supply—has caused water tables in the region to fall drastically. In the 1930s, wells encountered plentiful water at a depth of about 15 meters; currently, they must be dug to depths of 45 to 60 meters or more. In places, the water table is declining at a rate of a meter a year, necessitating the periodic deepening of wells and the use of ever-more-powerful pumps. It is estimated that at current withdrawal rates, much of the aquifer will run dry within 40 years. The situation is most critical in Texas, where the climate is driest, the greatest amount of water is being pumped, and the aquifer contains the least water. It is projected that the remaining Ogallala water will, by the year 2030, support only 35 to 40 percent ofthe irrigated acreage in Texas that is supported in 1980. The reaction of farmers to the inevitable depletion of the Ogallala varies. Many have been attempting to conserve water by irrigating less frequently or by switching to crops that require less water. Others, however, have adopted the philosophy that it is best to use the water while it is still economically profitable to do so and to concentrate on high-value crops such as cotton. The incentive of the farmers who wish to conserve water is reduced by their knowledge that many of their neighbors are profiting by using great amounts of water, and in the process are drawing down the entire region’s water supplies. In the face of the upcoming water supply crisis, a number of grandiose schemes have been developed to transport vast quantities of water by canal or pipeline from the Mississippi, the Missouri, or the Arkansas rivers. Unfortunately, the cost of water obtained through any of these schemes would increase pumping costs at least tenfold, making the cost of irrigated agricultural products from the region uncompetitive on the national and international markets. Somewhat more promising have been recent experiments for releasing capillary water (water in the soil) above the water table by injecting compressed air into the ground. Even if this process proves successful, however, it would almost triple water costs. Genetic engineering also may provide a partial solution, as new strains of drought-resistant crops continue to be developed. Whatever the final answer to the water crisis may be, it is evident that within the High Plains, irrigation water will never again be the abundant, inexpensive resource it was during the agricultural boom years of the mid-twentieth century. ▉托福TPO3阅读Passage2题目： Question 1 of 14 According to paragraph 1, which of the following statements about the High Plains is true? A. Until farmers and ranchers settled there in the 1880s, the High Plains had never been inhabited.. B. The climate of the High Plains is characterized by higher-than-average temperatures.. C. The large aquifer that lies underneath the High Plains was discovered by the Ogallala Sioux Indians.. D. Before the early 1900s there was only a small amount of farming and ranching in the High Plains..。
托福听力tpo30原题答案解析lecture2paleontology
今天，环球托福为大家带来了托福听力TPO30原题答案解析Lecture2 paleontology，大家可以配合托福听力TPO30原题答案解析Lecture1一起来读学习。
以提高学习效率，环球托福祝你早日成功！托福听力TPO30原题What does the professor mainly discuss?A. How the parenting behavior of Oviraptors may have differed from that of other dinosaursB.Evidence that parenting behavior in birds may have originated with dinosaursC.Physical traits shared by dinosaurs, crocodiles, and birdsD.The changing attitudes of the public toward dinosaurs答案：B解析： We will be looking at dinosaurs parenting behavior. 与这个 Topic Sentence 相关的只有B项。
What is the professor's attitude toward the name "Obiraptor" ? Click on 2 answers.A. It accurately represents the behavior of the dinosaurB.It resulted from an incorrect translation of the original Latin termC.It was based on a misunderstanding of the fossil evidenceD.It influenced popular attitudes toward dinosaurs答案：CD解析： He assumed the dinosaur was stealing the eggs...... Leave generally negative influence on such dinosaurs......the oviraptor was probably taking care of the eggs.According to the professor, what behavior is very rare among reptiles?A.Parenting of the young by malesying eggs in a nestC.Returning to the same nest site year after yearD.Stealing eggs from the nests of other reptiles答案：A解析：Well, exclusive care by the male parent is much less common, but it dose occur......males contribute to parental care in fewer than 5% ...... It is even less frequent on reptiles. 说明有父亲看护孩子很少见。
托福TPO34阅读Passage2原文文本+题目+答案解析
为了帮助大家高效备考托福，为大家带来托福TPO34阅读Passage2原文文本+题目+答案解析，希望对大家备考有所帮助。
The Development of Steam Power 蒸汽机的发展 By the eighteenth century,Britain was experiencing a severe shortage of energy.Because of the growth of population,most of the great forests of medieval Britain had long ago been replaced by fields of grain and hay.Wood was in ever-shorter supply,yet it remained tremendously important.It served as the primary source of heat for all homes and industries and as a basic raw material.Processed wood(charcoal)was the fuel that was mixed with iron ore in the blast furnace to produce pig iron(raw iron).The iron industry’s appetite for wood was enormous,and by 1740 the British iron industry was stagnating.Vast forests enabled Russia to become the world’s leading producer of iron,much of which was exported to Britain.But Russia’s potential for growth was limited too,and in a few decades Russia would reach the barrier of inadequate energy that was already holding England back. 在18世纪之前，英国正在经历一次严重的能源短缺。