必修四UNIT 2课时作业 带答案
Unit2课时作业Ⅰ
Ⅰ.单词拼写
1．Dr Y uan is now c__ circulating______ his knowledge in many parts of the world.
2．After his stay at the seaside in the summer holidays, the boy looked s__ sunburnt______.
3．Jiaxing’s population e__ expanded ______ rapidly in the 1980s.
4．A lot of the grain in China has been e__ exported ______ to foreign countries.
5．They couldn’t afford to __ equip ______(装备) their laboratories properly because of lack of money.
6．Yuan Longping has d__ devoted ______ himself to finding ways to raise rice output.
7．People are __ confused ______(困惑的) about all the different labels on food these days.
8．Her unexpected arrangements ___ upset _____(搞乱)all our plans.
9．The s__ struggle ______ for independence was long and hard.
10．According to the government’s _ statistics _______(统计) ，the GDP in our country has risen by 11 percent this year. Ⅱ.选词填空
expand，struggle，free，hungry，satisfy，export，sunburn，equip
1．Many people were too poor to buy the food they needed，so most of them died of __ hunger ______
2．Now no one can restrict our __ freedom ______ of speech，so we can say what we want.
3．That answer won’t __ satisfy ______ him.
4．Sydney’s population __ expanded ______ rapidly in the 1960s.
5．Look, she ___ is struggling _____________ to her feet.
6．Our country _ exports _______ a great deal of coal to Japan every year.
7．Judging from his _ sunburnt _______ face and arms, he works in the open air.
8．The soldiers were well _ equipped _______ with weapons and ready to start.
Ⅲ.单项填空
1．What he has done is far from ________.
A．satisfactory B．satisfiedC．satisfaction D．satisfy
[解析]far from satisfactiory意为“完全不能令人满意”。[答案] A
2．As there was no one to help him，the old man had to ________ his feet though he had a bad fall.
A．jump to B．struggle toC．raise to D．struggle on
[解析]struggle to one’s feet为固定词组，意为“挣扎着站起来”。[答案] B
3．________ our English teacher, our English has been greatly improved.
A．Thanks to B．Thank forC．But for D．Except for
[解析]只有A项表示的意思才能使句意连贯。C项意为“要不是”，与句意不符。[答案] A
4．Nick is looking for another job because he feels that nothing he does ________ his boss.
A．serves B．satisfiesC．promises D．supports
[解析]由题意“令……满意”来看，只有B项合适。A项意为“为……服务”；C项意为“许诺”；D项意为“支持”。[答案] B
5．I hope it will be fine this Sunday.________，we’ll go for an outing.
A．If not B．What ifC．Why not D．If so
[解析]根据前后句意得知，空格中所填的内容应表达“如果那样”的意思。[答案] D
6．We want to build another teaching building. Now we are ________ money.
A．need B．neededC．in need of D．in need
[解析]in need of为介词短语，其后可接名词，而D项相当于副词，其后不能接名词。[答案] C
7．She is studying hard now，________ passing the college entrance examination and going to college.
A．with the hope of B．in hopes ofC．in the hope of D．all the above
[解析]A、B、C三项的表达形式都是正确的。[答案] D
8．The news ________ that Mr Smith was trying to ________ his business all over the world.
A．expanded; spread B．expanded; expandC．spread；spread D．spread；expand
[解析]spread指消息等“传播”；expand意为“扩大；发展”。[答案] D
9．The school ________ ten courses which will ________ you to get a good job in the future.
A．equips；offer B．offers；equipC．equips；equip D．offers；offer
[解析]offer提供；equip sb.使某人具有……的能力。[答案] B
10．—I wonder how you’ve lived through all these years.
—I would rather ________ you.
A．not tell B．not to tellC．don’t tell D．not telling
[解析]would rather not do sth.不想做某事。[答案] A
11．He was so ________ to hear of her illness that he couldn’t sleep.
A．worrying B．disturbedC．interrupted D．exciting
[解析]由从句中“睡不着觉”可以看出他不安的心情。[答案] B
12．Paul doesn’t have to be made ________；he always works hard.
A．learn B．to learnC．learned D．learning
[解析]本题中make用作被动语态，故其补足语的不定式符号to要带上。[答案] B
13．John made ________ that he would marry Rose, which surprised everyone present.
A．it known B．that clearC．them known D．it know
[解析]it为形式宾语，known为宾语补足语，that从句为真正的宾语。[答案] A
14．The struggle ________ independence was long and hard.
A．with B．againstC．for D．on
[解析]表示“为……而斗争”struggle后应用for。[答案] C
15．The experts advise ________ our army ________ modern weapons.
A．to equip；with B．equipping；withC．to equip；for D．equipping；for
[解析]advise后接动名词，equip与介词with搭配。[答案] B
Ⅳ.阅读理解
For thousands of years, man has enjoyed the taste of apples. Apples, which are about 85 percent water, grow almost everywhere in the world but the hottest and coldest areas. Among the leading countries in apple production are China，France and the United States.
There are various kinds of apples, but a very few make up the majority of those grown for sale. The three most common kinds grown in the United States are Delicious，Golden Delicious, and Mcintosh.
Apples are different in colour, size and taste. The colour of the skin may be red, green, or yellow. They have various sizes, with Delicious apples being among the largest. The taste may be sweet or tart (酸的). Generally, sweet apples are eaten fresh while tart apples are used to make applesauce(苹果酱)．
Apple trees may grow as tall as twelve metres. They do best in areas that have very cold winters. Although no fruit is yielded during the winter, this cold period is good for the tree.
1．It can be learned from the text that Delicious apples are ________.
A．grown in France B．sold everywhereC．very big D．quite sweet
[解析]细节理解题。由“They have various sizes，with Delicious apples being among the largest.”可知。[答案] C 2．Cold winter weather is good for ________.
A．the growth of apple treesB．producing large applesC．improving the taste of applesD．the increase of water in apples [解析]句意理解题。由文中最后一句“Although no fruit is yielded during the winter, this cold period is good for the tree.”可知，冬季不产苹果，因此与苹果的大小与味道等无关。[答案] A
3．China, France and the United States are considered to ________.
A．be large producers of applesB．be large producers of applesauceC．have the longest history in apple production D．have the coldest winter among apple producing countries
[解析]细节理解题。由第一段第三句“Among the leading countries in apple production are China，France and the United States.”可知。[答案] A
4．The underlined word “yielded” in the last paragraph means ______.
A．improved B．increasedC．produced D．sold[答案] C
课时作业Ⅱ
Ⅰ.选词填空
1．It was several weeks before he was completely _ free from _______ pain.
2．The farmers want to make sure the soil __ is richer in ______ minerals than before.
3．As we all know, acid rain will _ cause damage to _______ crops.
4．Eating too much fat easily _ leads to _______ high blood pressure.
5．___ To our regret _____，the Rocket failed the game by 89—91 at last five seconds.
6．Some schools _ insist on _______ their students wearing school uniform.
7．He ___ focused _____ all their attention __ on ______ finding a solution to the problem.
8．He went on holiday by the seaside and soon __ built up ______ his health.
9．Would you like to give _ comments on _______ my work?
10．They often change the kind of crops in each field __ every few years ______.
Ⅱ.完成句子
1．学习而不实践是没有好处的。
It is no good _ learning without practice __
2．你花园里的花需要浇水。
The flowers in your garden want __ watering/to be watered ___.
3．我们不允许在办公室里吸烟。
We don’t allow _____ smoking in the office ___.
4．向她道歉是没有用的。
It’s no use __ apologizing to her ___.
5．我后悔上学的时候没有刻苦学习。
I regret __ not having studied hard at school ___.
Ⅲ.单项填空
1．The twin sisters are so alike that I often ________ her ________ her sister.
A．confuse; to B．confuse; by C．confuse; and D．confuse; for
本题考查confuse...and/with...“将……与……混同；将……与……混淆”这一搭配。C
2．They failed to pass the exam last time. I regretted ________ them.
A．to be not able to helpB．being not able to helpC．not being able to helpD．not be able to help
[解析]本句句意为：上次他们考试不及格，我很后悔没能帮他们。regret to do sth.对将要说的话或做的事而感到遗憾；regret doing sth.对已经做过的事表示后悔。not一般放在不定式或v.-ing之前。[答案] C
3．I don’t regret ________ even if it might have upset her.
A．to tell her what I thoughtB．to have told her that I thought
C．telling what I thoughtD．telling her what I thought
[解析]本句句意为：即使或许会让她难过，我也不后悔把我所想的告诉了她。regret doing sth.对已经做过的事表示后悔。[答案] D
4．On land many objects prevent sound ________ very far.
A．to travel B．travelC．from traveling D．to traveling
[解析]本题考查v.-ing充当介词的宾语。此题为prevent...from...结构。[答案] C
5．By ________ , water can be changed into gas.
A．heating B．being heatedC．having heated D．heated
[解析]本题考查v.-ing充当介词的宾语。又因为heat与water在逻辑上为动宾关系，故用v.-ing的被动形式。[答案] B
6．I remembered ________ this person somewhere before.
A．seeing B．having been seenC．seen D．to see
有些动词和动词词组后既可接不定式也可接v.-ing作宾语，但意思不同。remember to do记住要做；remember doing 记得曾做过。本句句意：我记得以前在某处见过这个人。 A
7．Mr Wang went on ________ in spite of illness.
A．to work B．workedC．working D．to be working
[解析]有些动词和动词词组后既可接不定式也可接v.-ing作宾语，但意思不同。go on to do接着做(另一件事)；go on doing继续做(同一件事)。本句句意：王先生虽然病了，但仍继续工作。[答案] C
8．It is no use ________ without thorough ________.
A．to read; understoodB．reading; understandingC．to read；understandD．read；to understand
[解析]本题第一个空考查It’s no use/good＋v.-ing句式。第二个空前为介词，后应跟v.-ing形式。[答案] B 9．Mike has got used ________ up late at night.
A．to sit B．sitC．to sitting D．sitting
本题考查get used to doing sth.“习惯做某事”。本句句意为：迈克已经习惯了熬夜。C
10．The heart keeps ________ all the time.
A．to beat B．beatingC．beaten D．to have been beating
[解析]keep后只跟v.-ing形式作宾语。[答案] B
11．His ________ look suggested that he was ________ about this matter.
A．confusing; confused B．confused; confusedC．confusing; confusing D．confused; confusing
本题考查confused和confusing的区别。confused adj.糊涂的，迷乱的，迷惑的；confusing adj.难以理解的；不清楚的。句意：他脸上迷惑的表情说明他对此事感到困惑。[答案] B
12．She stopped ________ confusion when everyone turned to look at her.
A．at B．aboutC．with D．in
此题考查名词与介词的搭配。in confusion意为“困惑地，迷茫地”。[答案] D
13．Lydia really regrets ________ out of high school. She has really had to struggle to make a living because of that decision.
A．drop B．to dropC．dropping D．dropped
[解析]本句句意为：莉迪亚后悔从高中辍学。由于那个决定她不得不艰难谋生。regret to do sth.对将要说的话或做的事而感到遗憾；regret doing sth.对已经做过的事表示后悔。 C
14．Besides ________，she is kind and tender.
A．beautiful B．being beautifulC．she beautiful D．is beautiful
[解析]besides为介词，后面跟v.-ing形式being，然后接形容词。[答案] B
15．We are both looking forward to ________ next week.
A．going on vacation B．go on vacationC．be going on vacation D．have gone on vacation
look forward to为一短语动词，意为“盼望”。to为介词，后需跟v.-ing形式作宾语。 A
Ⅳ.完形填空
One day, my eldest daughter came home after school, and hardly had she seen me when she told me that she had joined the drama(戏剧) club at school and started acting. This __1__ aspect of her personality surprised and __2__ me, for she was usually a very quiet and private teenager. On the night of her first public __3__，I sat in the front row. Unable to afford to buy roses, I myself __4__ for her a lovely bouquet(花束) of mixed flowers. “What are you doing？” asked my son. “Don’t you want to send to your sister something __5__ our congratulations？”
When the play __6__ and the performers lined up across the stage for their first bows, my son ran up and handed his sister the __7__. She positively felt happy and excited. Yet when the curtains __8__ and then reopened for the performers’ __9__ bows，she reappeared __10__ the bouquet. I said to myself, “Why didn’t she __11__ the bouquet？” Perhaps she
felt __12__ that she hadn’t received roses as some of the other actresses had. When I felt I’d let her down, __13__ filled my eyes. Then I __14__ that all the other actresses appeared with __15__ bunches of flowers in their arms. I __16__ my daughter had broken apart her bouquet __17__ all her friends had flowers to carry on stage for the final applause.
In one wonderful moment, her small act of __18__，like magic，encouraged me，a divorced mother. She had learned to do more __19__ less. She had come through the pain caused by my __20__. So would her brother and sister. And so would I.
在经历了父母离异的痛苦后，作者的女儿从一个喜欢孤独的人变成了一个开朗的、富有爱心的人，她愿意用自己微薄的力量去帮助身边的人。
1．A.strange B．well-knownC．natural D．new
女儿平时喜欢一个人独处，如今却要参加戏剧俱乐部，这是她性格中新的(new)一面。D
2．A.delighted B．annoyedC．disturbed D．discouraged
[解析]女儿性格的变化使作者既惊奇又高兴(delighted)。[答案] A
3．A.concert B．performanceC．practice D．training
由下文对演出的描述可知，那天晚上女儿和同伴们第一次登台演出(performance)。 B
4．A.made B．borrowedC．asked D．looked
[解析]“我”亲手为女儿制作了(made)花束。[答案] A
5．A.hoping B．wishingC．expressing D．replacing
[解析]expressing congratulations表示祝贺。[答案] C
6．A.started B．endedC．stopped D．continued
[解析]演出结束(ended)时，演员们向观众鞠躬致意。[答案] B
7．A.coshs B．cardsC．flowers D．congratulations
[解析]由上一段中的“Don’t yon want to send to your sister something...”可知，作者的儿子为他的姐姐送上了花(flowers)。[答案] C
8．A.opened B．roseC．faded D．closed
[解析]根据本句中的reopened可知，此空应填closed。[答案] D
9．A.individual B．professionalC．final D．informal
[解析]此时全体演员最后一次(final)鞠躬致意。[答案] C
10．A.around B．withoutC．for D．by
[解析]联系下文作者的心理活动可知，女儿手里没有(without)持花。[答案] B
11．A.accept B．receiveC．refuse D．offer
[解析]accept(主观上)接受。[答案] A
12．A.satisfied B．disappointedC．pleased D．tired
作者推测女儿因为没有像其他演员一样收到玫瑰花而感到失望(disappointed)。 B
13．A.cheers B．smilesC．fears D．tears
[解析]作者认为自己让女儿丢脸了，因而内疚流泪(tears)。[答案] D
14．A.studied B．wonderedC．watched D．noticed
[解析]notice注意到。[答案] D
15．A.small B．oldC．large D．beautiful
[解析]作者注意到(noticed)其他所有演员手里都拿着一小(small)束花。[答案] A
16．A.recalled B．realizedC．regretted D．remembered
[解析]作者意识到了(realized)女儿没捧花束的真正原因。[答案] B
17．A.as though B．even itC．so that D．in case
[解析]为了与其他演员分享喜悦，女儿将花束拆分给其他演员，以便(so that)他们都能手持鲜花谢幕。[答案] C 18．A.kindness B．happinessC．silliness D．loneliness
[解析]女儿将花束拆分给其他演员是善良(kindness)的举动。[答案] A
19．A.or B．andC．with D．than
[解析]作者的女儿学会了以(with)少去成就多。[答案] C
20．A.strictness B．dissatisfactionC．illness D．divorce
作者的女儿已经从父母离异(divorce)的痛苦中走出来了。本段第一句中的“a divorced mother”对此空有提示。 D 课时作业Ⅲ
Ⅰ.单词拼写
1．He is __ sunburned ______(晒黑) from a day on the beach.
2．The s_ struggle _______ for independence was long and hard.
3．There is h_ hunger _______ in all the places where the crop was spoilt by the flood.
4．The business has e_ expanded _______ from having one office to having twelve.
5．He didn’t smile at all; it suggested that he wasn’t s_ satisfied _______ with us.
6．They __ led ______(过着) a happy life after marriage.
7．Our school is e_ equipped _______ with modern teaching equipment.
8．Cooled air is _ circulated _______(循环) throughout the building.
9．The children enjoyed the f_ freedom _______ of the school holidays.
10．China _ exports _______(出口) to many other countries regions.
Ⅱ.用所给词的适当形式填空
1．_ Walking _______(walk) is a good form of exercise for both men and women.
2．The hunter took careful aim and shot at the bird, but it was lucky enough to miss __ being shot____(shoot)．
3．_ Finding __(find) a job in such a big company is always beyond his widest dream.
4．All the boys are looking forward to _ visiting (visit) the super hybrid rice fields developed by Dr. Yuan Longping. 5．He wanted _ to experiment _ (experiment) with scientific methods of farming.
6．Once your business becomes international, _ flying ___(fly) constantly will be part of your life.
7．While shopping, women sometimes can’t help __ being persuaded _ (persuade) into buying more things than necessary. 8．—Maybe you have forgotten ___ to post _____(post) my letter?
—How could I? I remember __ putting ______(put) the letter into the letter box.
9．—What made Jane upset?
—__ Losing ______(lose) the ring her husband bought her for her birthday.
10．—Do you think it of any use _ talking _______(talk) with him any more?
—We are wasting our time _ trying _______(try) to persuade him to give up his foolish idea.
Ⅲ.单项填空
1．—Some more wine?
—Thank you.________. I have to drive home.
A．With pleasure B．I’d rather notC．That would be nice D．Just what I needed
[解析]交际用语题。从上文看别人是在劝酒“Some more wine？”由下文“I have to drive home”可知不能再喝酒了，因此选B。[答案] B
2．It is ________ that two and two make four.
A．certain B．sureC．suitable D．necessary
[解析]2＋2＝4是一个客观事实，因此要用certain表“肯定”；sure“真的”；suitable“合适的”；necessary“必要的”，均不合乎题意。[答案] A
3．If water is heated, it will ________.
A．expand B．spreadC．develop D．increase
[解析]词义辨析。句意为：如果水被加热的话，就会expand“蒸发”，而不是“传播”(spread)，“发展”(develop)，“增加”(increase)。[答案] A
4．She told me that she was not ________ with my examination results.
A．inspired B．surprisedC．satisfied D．excited
“对……满意”用be satisfied with...；通过句意来看，应该是他对我们考试结果不满意，所以选C。
5．If I ruled the world, I would ________ the world ________ everything that is bad.
A．get rid of; by B．be rid of; byC．rid; of D．get rid; of
[解析]句意为：要是我主宰世界，我就会把世界上一切坏的东西去除。rid...of“除去”。[答案] C
6．The experts advise ________ our army ________ modern weapons.
A．to equip; with B．equipping; withC．to equip; for D．equipping; for
句意为：专家建议我们要用最好的装备来武装军队。“建议某人做某事”advise sb.doing sth.，“装备”equip with B 7．We found several ________ of rice near the hole. The mice may have stored a lot of ________ in the hole. A．grain; grain B．grains; grainsC．grain; grains D．grains; grain
[解析]词义考查题。grains，质量单位；grain“种子，细穗”。[答案] D
8．Our school covers an area of 400 acreage, which is ________ as yours.
A．twice as big B．twice biggerC．twice the size D．twice the big
考查倍数的表达法。句意为：我们学校占地四百亩，是你们的两倍。可以用twice as big as来表示。A
9．There ________ a temple on the side of the mountain, didn’t there?
A．would be B．would haveC．used to have D．used to be
[解析]used to过去常常。[答案] D
10．The war made ________ impossible for the scientist to go on with his research.
A．him B．itC．this D．that
[解析]it在这里作形式宾语。[答案] B
11．If you try to learn too many things at a time at the beginning, you may ________.
A．have confused B．have to be confusedC．get confused D．get confusing
[解析]句意为：如果你在开始就一次学习很多东西的话，你肯定会有很多困惑。get confused“困惑”。
[答案] C
12．We’ll do ________ the party calls upon us to do.
A．no matter what B．whateverC．however D．whenever
[解析]句意为：我们坚决按照党要求我们的去做。很明显，这里缺少宾语，是一个名词性从句，因此用whatever。no matter what不能引导名词性从句。[答案] B
13．As is known to all, oranges are ________ Vitamin C.
A．rich in B．poor withC．short of D．good for
[解析]常识性问题。橘子富含维生素是都知道的，所以用rich in“丰富”。A
14．Do you know that ________ with wise men improves your mind?
A．chat B．chatsC．chatted D．chatting
所填写的部分是宾语从句，在从句中又缺少主语，所以用动名词的形式来作主语。 D
15．When I said that some people are stupid I was not ________ you.
A．talking to B．referring toC．turning to D．listening to
句意为：当我说有人笨的时候，并不是指你。refer to“提及，涉及”。[答案] B
Ⅳ.书面表达
根据下列提示为21st Century Teens写一篇题为Development of agriculture in China的小短文。
1．中国是一个有13亿人口的大国。
2．在过去的二十年间，中国发生了巨大的变化，尤其在农业方面。
3．中国仅有世界上7%的土地，却成功地养活了世界上22%的人口。
4其耕地(farming land)的灌溉面积是世界上最大的。种植了世界上1/3的水稻。渔业也非常发达，淡水鱼随处可见。
5．废弃的蔬菜(vegetable waste)被用来养猪、养鸡；人和动物的粪便(waste)产生的气体被用来供热和做饭。6．如果世界上其他地方也像中国一样重视和发展农业，就不会再有饥饿。
Development of agriculture in China
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[答案]China is a large country with a population of 1.3 billion. In the past two decades, great changes have taken place in China especially in agriculture. China has only 7% of the world’s land but successfully feeds 22% of the world’s population. It has the largest irrigated area of farming land in the world and grows a third of the rice crop. Fish farming is also well developed and fresh-water fish can be seen everywhere. Vegetables waste is used to feed pigs and chickens. Gas produced from human and animals waste is used for heating and cooking. If the rest of the world also think much of and develop agriculture like China, there would be no starvation.
人教版高中生物必修一、必修二课时训练：第8练细胞膜和细胞核
1．下列选项中，不属于细胞膜功能的是 () A．控制物质进出细胞 B．将细胞与周围环境分隔开 C．进行细胞间的信息交流 D．控制细胞的代谢 2．(2019·枣庄调查)下列生理过程中，需要依赖于细胞膜上的受体才可完成的是() A．氨基酸通过细胞膜进入组织细胞被利用 B．高等植物细胞间通过胞间连丝相互连接 C．垂体细胞分泌生长激素 D．神经递质作用于突触后膜引发兴奋或抑制 3．下列过程不能体现细胞膜的流动性特点的是() A．蛙红细胞的分裂 B．唾液腺细胞分泌淀粉酶 C．植物细胞质壁分离 D．肝细胞膜上的糖蛋白识别胰岛素
4．下列有关细胞间信息交流的叙述中，正确的是() A．细胞间信息交流是细胞膜的功能之一，体现了细胞膜的选择透过性 B．神经递质与突触后膜上的受体结合后，即被受体转运到突触后膜上，使后膜兴奋或抑制 C．与胰岛素和甲状腺激素结合的受体可能相同，也可能不同D．细胞间信息交流的方式多种多样，可以是细胞接触传递信息，也可以通过介质传递 5．(2019·衡阳八中质检)如图表示细胞膜的亚显微结构，其中a和b 为物质的两种运输方式，下列对细胞膜结构和功能的叙述错误的是() A．若图示为肝细胞膜，则尿素的运输方向是Ⅱ→Ⅱ B．细胞间的识别、免疫、细胞的癌变与Ⅱ有密切的关系 C．适当提高温度将加快Ⅱ和Ⅱ的流动速度 D．b过程不需要A TP，a过程未体现膜的选择透过性这一生理特性6．(2019·长沙月考)下列关于细胞膜的流动镶嵌模型说法正确的是() A．罗伯特森利用光学显微镜提出了“亮—暗—亮”的三明治结构是一
种静态模型 B．利用放射性同位素标记法将小鼠和人细胞膜上的蛋白质做标记的实验，证明了细胞膜具有一定的流动性 C．细胞膜上绝大多数的蛋白质和磷脂双分子层都具有一定的流动性D．欧文顿利用了化学上的“相似相容原理”解决了脂溶性物质为什么更容易进入细胞，是因为细胞膜上具有大量的磷脂和少量的固醇7．(2019·枣庄学情调查)关于细胞核的叙述，正确的是() A．细胞核行使遗传功能的结构是核孔 B．核糖核苷酸只能通过核孔进入细胞核 C．细胞核控制细胞所有的遗传特性 D．没有细胞核也能合成蛋白质 8．心房颤动(房颤)是临床上最常见并且危害严重的心律失常疾病，最新研究表明，其致病机制是核孔复合物的运输障碍(核孔复合物是位于核孔上与核孔的结构和功能密切相关的物质)，据此分析正确的是() A．核膜由两层磷脂分子组成，房颤的成因与核膜内外的信息交流异常有关 B．核孔运输障碍发生的根本原因可能是编码核孔复合物的基因发生
英语必修五课文翻译
必修五课文原文翻译 unit 1约翰·斯诺战胜“霍乱王” 约翰·斯诺是伦敦一位著名的医生——他的确医术精湛，以至于成了照料维多利亚女王的私人医生。但当他一想到要帮助(那些)得了霍乱的普通百姓时，就感到很受鼓舞。霍乱在当时是最致命的疾病。人们既不知道它的病因，也不懂如何治疗。每次爆发霍乱时就有成千上万惊恐的人病死。约翰·斯诺想面对这一挑战，解决这一问题。他知道在找到病源之前，霍乱疫情是无法控制的。 他对霍乱致人死地的两种推测产生了兴趣。第一种看法是霍乱病毒在空气中繁殖，像一股危险气体在空中到处漂浮，直到找到病毒的受害人。第二种看法是人们是在吃饭时把这种病毒引入体内的。病毒从胃部开始迅速殃及全身，患者就会很快地死去。 约翰·斯诺推测第二种说法是正确的，但需要有证据。因此在1854年伦敦再次爆发霍乱时，他就着手准备对此调研。当霍乱在贫民区迅速蔓延时，约翰·斯诺开始搜集信息。他发现特别在两条街上霍乱流行得很严重，以至于10天内就有500多人死亡。他决心查清原因。 他首先在地图上标注出所有死者曾住过的确切地点。该图提供了一条说明霍乱起因的很有价值的线索。许多死者都住在布洛德街上的水泵附近(尤其是这条街上的16、37、38和40号)。他还发现有些住户(如布洛德街20号和21号及剑桥街8号和9号)却无人死亡。他未预料到这种情况，于是他做了进一步调查。他发现这些人是在剑桥街7号的酒馆里打工。酒馆为他们供应免费啤酒，因此他们没喝布洛德街水泵里的水。看来水是罪魁祸首。 接下来，约翰·斯诺调查了这两条街上的水源。他发现水来自于河里，这条河被伦敦排出的脏水污染了。约翰·斯诺立即告诉布洛德街上惊慌失措的人们拆掉水泵的把手，这样水泵就用不成了。不久，疫情就开始得到缓解。他证明了霍乱是通过细菌传播而非气团传播。 在伦敦的另一地区，他从另外两例与布洛德街疾病爆发有关的死亡病例中得到了有力的证据。一个妇女，从布洛德街搬走了，但她非常喜欢水泵的水，她让人每天从水泵给她家送水。她和她的女儿在喝了这些水后，都死于霍乱。利用这个额外证据，约翰·斯诺就可以很有把握地宣布污染水携带病菌。 为防止这种情况再度发生，约翰·斯诺建议，所有水源都要经过检测。供水公司也得到指示再也不能让人们接触污染水了。“霍乱王”终于被击败了。
人教版高二数学必修五：课时作业11有答案
课时作业(十一) 1．在等差数列{a n }中，已知a 1＝2，a 2＋a 3＝13，则a 4＋a 5＋a 6等于( ) A ．40 B ．42 C ．43 D ．45 答案 B 解析 ∵a 2＋a 3＝13，∴2a 1＋3d ＝13.∵a 1＝2，∴d ＝3. 而a 4＋a 5＋a 6＝3a 5＝3(a 1＋4d )＝42. 2．在等差数列－5，－312，－2，－1 2，…中，每相邻两项之间插入一个数， 使之组成一个新的等差数列，则新数列的通项公式为( ) A ．an ＝34n －23 4 B ．an ＝－5－3 2(n －1) C ．an ＝－5－3 4(n －1) D ．an ＝5 4 n 2－3n 答案 A 解析 首项为－5，公差为－312＋52＝3 4， ∴an ＝－5＋(n －1)·34＝34n －23 4 . 3．若a ，b ，c 成等差数列，则二次函数y ＝ax 2＋2bx ＋c 的图像与x 轴交点的个数是( ) A ．0 B ．1 C ．2 D ．1或2 答案 D 解析 ∵a 、b 、c 成等差，∴2b ＝a ＋c . ∴Δ＝(2b )2－4ac ＝(a ＋c )2－4ac ＝(a －c )2≥0.
4．数列{an }中，a 1＝15,3an ＋1＝3an －2，那么该数列中相邻两项的乘积为负数的是( ) A ．a 21和a 22 B ．a 22和a 23 C ．a 23和a 24 D ．a 24和a 25 答案 C 解析 由3an ＋1＝3an －2可知{an }为等差数列，又a 1＝15， ∴an ＝15＋(n －1)·(－23)＝－23n ＋473＝47－2n 3. 令an ·an ＋1<0，即47－2n 3· 47－n ＋ 3<0. 可得452
新人教版英语必修三Unit2 Grammar课时作业含答案
《Unit 2 Healthy eating Grammar & Writing》Ⅰ.用适当的情态动词完成下列句子
Thank you for your letter. I don't think I 1.________ give you any advice. I don't think the manager 2.________ trust you. It sounds as if he has decided that you 3.________ be the thief. Do you have to continue working at this company? Maybe you 4.________ find another job where the people are friendly. I think you 5.________ enjoy that more. If you stay at the meat factory, you 6.________ not be able to be happy. Besides, if you stay, the thief 7.________ do something bad to you. I don't think that 8.________ be very pleasant. If he played a trick on you, the manager 9.________ say you were the thief and call in the police. That 10.________ have serious results. I think the best thing you 11.________ do now is to look for another job and hope that it 12.________ turn out better. Yours sincerely， Mike 答案：1.can 2.will 3.must 4.should/ought to/can/need 5.may/might/will 6.will 7.may/will/might 8．will 9.might/would 10.may/will/might 11．can/should/ought to/need 12.will/would Ⅴ.阅读理解 Today fast food restaurants are very popular. One famous name is Harry's Hamburgers. Harry's Hamburgers come from America and have been in business for thirty years. There are about 5,000 Harry's Hamburgers in different countries. The food is the same everywhere. In London, New York or Paris people eat the same hamburgers and drink the same drinks. Hamburger Harry is a special friend of children everywhere. He goes to schools and talks to pupils. He goes into different classrooms, sits down on the carpet or at the desk and asks the pupils to relax. Then he begins his talk. Harry teaches children about litter. “Don't throw your boxes on the floor in my restaurants，” he says. “And don't throw my bags away in the street. If you see boxes and bags in the street, pick them up and throw them into the bin (垃圾箱)．” Hamburger Harry visits children in hospitals and tells them funny stories. His restaurants give wonderful birthday parties. Parents telephone the restaurant or go there. They choose a good day for the party, arrange the food and drink and send invitations to friends. Hamburger Harry sometimes comes to the party with a bag of presents and a big birthday cake. The boys and girls sit round the tables and eat all their favorite food. They all wear paper hats and party badges(徽章). Hamburger Harry dresses in green, red and yellow and he wears two big badges. He works hard at the party. He tells jokes, sings songs and gives everyone a present. The children get colored pencils, balloons and books to draw on. They always have a good time. Their parents enjoy the party too because they don't prepare the tables and they don't cook the food. They don't have to clean the restaurant after the party. All they do is pay the bill. 1．Harry's hamburgers are sold ________. A．without drinks B．at a high price C．in the same style D．with different tastes 2．If a child holds a birthday party at Harry's restaurant, Harry may ________. A．give a big cake to the child as a gift B．ask his workers to sing for the child C．play a joke on the child for fun D．decorate the restaurant with balloons
人教新课标高中生物必修二第1节 孟德尔的豌豆杂交实验(一) 第1课时 提高练习
第1节孟德尔的豌豆杂交实验（一）（第1课时）1．孟德尔通过杂交实验发现了一些有规律的遗传现象，通过对这些现象的研究提出了遗传的基本规律。在下列各项中，哪项不是出现这些有规律遗传现象不可缺少的因素（）A．F1体细胞中各遗传因子表达的机会相等 B．F1自交后代发育成活的机会相等 C．各遗传因子在F2体细胞中出现的机会相等 D．每种类型雌配子与每种类型雄配子相遇的机会相等 2．下表是桃树花色的三组遗传实验结果，据此分析下列叙述错误的是（） A．组合①的红花亲本与F1红花植株均为杂合子 B．组合②③均可判断这对性状的显隐性关系 C．组合③的F1中纯合红花所占比值为1/4 D．组合③，F1红花中，杂合子所占比值为1/2 3．现有两块农田，农田A混合种植了杂合高茎豌豆和矮茎豌豆，而农田B混合种植了甜玉米和杂合非甜玉米。豌豆的高茎和矮茎与玉米的甜和非甜均受一对遗传因子控制，不考虑其他植物，下列相关叙述，错误的是（） A．豌豆的高茎对矮茎为显性，玉米的非甜对甜为显性 B．农田A中矮茎豌豆所结种子长成的植株均表现为矮茎 C．农田B中杂合非甜玉米所结种子长成的植株1/4为甜玉米 D．农田A中各植株自花受粉，而农田B中各植株随机受粉 4．已知豌豆种子子叶的黄色与绿色是一对遗传因子Y、y控制的，用豌豆进行下列遗传实验，具体情况如下： 实验一实验二
P 黄色子叶（甲）×绿色子叶（乙）P 黄色子叶（丁） ↓↓自交 F1黄色子叶（丙）绿色子叶F1黄色子叶（戊）绿色子叶 1 ： 1 3 ：1 请分析回答： （1）用豌豆做遗传实验容易取得成功的原因之一是________________________。 （2）从实验____可判断这对相对性状中________是显性性状。 （3）实验二黄色子叶戊中能稳定遗传的占________。 （4）实验一子代中出现黄色子叶与绿色子叶的比例为1:1，主要原因是黄色子叶甲产生的配子种类及其比例为______。 （5）实验中一黄色子叶丙与实验二中黄色子叶戊杂交，所获得的子代黄色子叶个体中不能稳定遗传的占_______。 5．豌豆花的腋生和顶生是一对相对性状，受一对遗传因子B、b控制。如下表是几组杂交实验结果。 根据以上实验结果，分析回答下列问题。 （1）根据组合______可判断出显性性状是______（填“顶生”或“腋生”）。 （2）组合二亲本的遗传因子组成是______和______，理论上其后代腋生豌豆中纯合子所占比例为______（填分数）。 （3）组合三后代的腋生豌豆中杂合子占______（填百分比）。
高二英语必修五第4单元课文翻译
高二英语必修五Unit 4课文翻译 Unit 4 Making the news Reading MY FIRST WORK ASSIGNMENT "Unforgettable", says new journalist 我的第一项工作任务“难以忘怀，”新闻记者说Never will Zhou Yang (ZY) forget his first assignment at the office of a popular English newspaper. His discussion with his new boss, Hu Xin (HX), was to strongly influence his life as a journalist. 周阳永远不会忘记他在一家畅销英文报纸的第一项工作任务。他同新上司胡欣的讨论对他的记者生涯必将产生强烈的影响。 HX: Welcome. We're delighted you're coming to work with us. Your first job here will be an assistant journalist. Do you have any questions? 胡：欢迎你，非常高兴你来参加我们的工作，你来这里首先就是当助理记者。有什么问题吗? ZY: Can I go out on a story immediately? 周：我可以马上去采访吗? HX: (laughing) That' s admirable, but I' m afraid it would be unusual ! Wait till you' re more experienced. First we'll put you as an assistant to an experienced journalist. Later you can cover a story and submit the article yourself.
红对勾·讲与练高中数学北师大必修五：课时作业 等差数列的概念和通项公式
课时作业3等差数列的概念和通项公式 时间：45分钟满分：100分 一、选择题(每小题5分，共35分) 1．已知数列{a n}的通项公式为a n＝2 011－2 012n，则此数列() A．是首项为2 011的等差数列 B．是首项为－1且公差为2 012的等差数列 C．是公差为2 011的递增等差数列 D．是首项为－1且公差为－2 012的递减等差数列 【答案】 D 【解析】a1＝－1，a n＋1－a n＝[2 011－2 012(n＋1)]－(2 011－2 012n)＝－2 012<0.故选D. 2．已知在数列{a n}中，a n＋1－a n＝2，且a1＝2，则这个数列的第10项为() A．18B．19 C．20 D．21 【答案】 C 【解析】由条件知{a n}是公差为2的等差数列，故a10＝a1＋9d ＝2＋9×2＝20. 3．在等差数列{a n}中，a1＋a5＝10，a4＝7，则数列{a n}的公差为() A．1 B．2 C．3 D．4 【答案】 B
【解析】∵a1＋a5＝10＝2a3， ∴a3＝5.故d＝a4－a3＝7－5＝2. 4．在等差数列{a n}中，a1＋a9＝10，a2＋a10＝14，则a4的值为() A．3 B．6 C．8 D．10 【答案】 A 【解析】由a1＋a9＝10，a2＋a10＝14得d＝2， ∵a1＋a9＝2a1＋8d＝10， ∴a1＝－3，∴a4＝－3＋3×2＝3. 5．已知递增的等差数列{a n}满足a1＝1，a3＝a22－4，则a n＝() A．2n B．2n－1 C．n－1 D．2n＋1 【答案】 B 【解析】设等差数列{a n}的公差为d(d>0)． 由a3＝a22－4得a1＋2d＝(a1＋d)2－4，即1＋2d＝(1＋d)2－4，d2＝4.又{a n}是递增数列，所以d＝2， 故a n＝a1＋(n－1)d＝1＋(n－1)·2＝2n－1. 6．设S n是数列{a n}的前n项和，且S n＝n2，则{a n}() A．是常数列B．是等差数列 C．是摆动数列D．非以上三种数列 【答案】 B
人教七年级上册英语unit2课时作业练习(含答案)
七年级上册英语unit2课时作业练 习 第1课时(Section A 1a-2d) 一、根据句意及首字母提示完成单词。 1.My father’s mother is my g. 2.My father’s father is my g. 3.My father’s sisters are my a. 3.My father’s sisters are my 4.Li Ming is my f.He is 10 years old. 4.Li Ming is my 5.She is my s. 二、选词填空。 his parents apples grandmother those 1.My father and my mother are my . 2.This is my https://www.360docs.net/doc/433941908.html, is Jack. 3.What are these? They are . 4.are my sisters. 5. Your mother’s mother is your . 三、用this，that，those或these填空。
1.is a ruler and is a pen. 2. –Are your friends? --Yes，they are. 3.—Are your cups? --No. These are her cups. 4.Dad，is my friend ，Kate. 5.—What’s over there? --It’s a school. 第2课时（Section A Grammar Focus –3c） 一、用be动词的适当形式填空。 1.I eleven. 2.-Is this your ball? --Yes ，it . 3.Who they? 4.“I”an English letter or an English word. 5.Here two red apples. 二、单项选择。 （）1.There are three in the basketball. A.potato B. book C.toy D. apples （）2.My mother gives a nice toy bike for my birthday. A. I B. me C. my D. mine
超级资源(共24套119页)人教版高一生物必修二(全册)同步练习 课后作业汇总
超级资源（共24套119页）人教版高一生物必修二（全册）同步练习课后作业汇总 孟德尔豌豆杂交实验（一）（总分：71分） 一．选择题(每题2分) 1．下列各对性状中, 属于相对性状的是（） A．狗的长毛和卷毛 B．棉花的掌状叶和鸡脚叶
C．玉米叶梢的紫色和叶片的绿色 D．豌豆的高茎和蚕豆的矮茎 2．“假说—演绎法”是现代科学研究中常用的一种方法, 下列属于孟德尔在发现基因分离定律时的“演绎”过程的是( ) A．生物的性状是遗传因子决定的 B．由F2出现了“3∶1”推测, 生物体产生配子时成对遗传因子彼此分离 C．若F1产生配子时成对遗传因子分离, 则测交后代会出现两种性状, 比例接近1∶1 D．若F1产生配子时成对遗传因子分离, 则F2中三种基因个体比接近1∶2∶1 3．狗的卷毛（A）对直毛（ａ）是显性, 判断一只卷毛狗是否是纯合体, 最好选用与它交配的狗是（） A．纯种卷毛 B．直毛 C．杂种卷毛 D．A．B．C都对 4．下列叙述中正确的是（） A.纯合体自交的后代是纯合体 B.杂合体自交的后代是杂合体 C.两种纯合体杂交其后代仍是纯合体 D.杂合体杂交的后代全是杂合体 5．杂合子高茎豌豆自交, 后代中已有16株为高茎, 第17株还是高茎的可能性是（）A．0 B．25% C．75% D．50% 6．将具有一对等位基因的杂合子, 逐代自交3次, 在F3代是纯合子的比例为（）A．1/8 B．7/8 C．7/16 D．9/16 7．水稻中非糯性(W)对糯性(w)为显性, 非糯性品系所含淀粉遇碘呈蓝黑色, 糯性品系所含淀粉遇碘呈红褐色。下面是对纯种的非糯性与糯性水稻的杂交后代进行观察的结果, 其中能直接证明孟德尔的基因分离定律的一项是 ( ) A．杂交后亲本植株上结出的种子(F1)遇碘全部呈蓝黑色 B．F1自交后结出的种子(F2)遇碘后, 3/4呈蓝黑色, 1/4呈红褐色 C．F1产生的花粉遇碘后, 一半呈蓝黑色, 一半呈红褐色 D．F1测交所结出的种子遇碘后, 一半呈蓝黑色, 一半呈红褐色 8．下列四组交配中, 能验证对分离现象的解释是否正确的一组是（） Ａ．ＡＡ×ＡａＢ．Ａａ×ａａＣ．Ａａ×ＡａＤ．ＡＡ×ａａ 9．基因型为ＡＡ的个体与基因型为ａａ的个体杂交产生的Ｆ1进行自交, 那么Ｆ2中的纯合子占Ｆ2中个体数的（） Ａ．２５％Ｂ．５０％Ｃ．７５％Ｄ．１００％ 10．基因分离定律表明, 杂合子（） A．不能稳定遗传, 自交后代有性状分离 B．不能稳定遗传, 自交后代无性状分离
【人教A版】2017版高中数学必修五：课时作业含答案2
课时作业(二) 1．在△ABC中，a＝2b cos C，则这个三角形一定是() A．等腰三角形B．直角三角形 C．等腰直角三角形D．等腰或直角三角形 答案 A 2．已知△ABC中，AB＝3，AC＝1，且B＝30°，则△ABC的面积等于() A. 3 2 B. 3 4 C. 3 2或 3 D. 3 4或 3 2 答案 D 3．在△ABC中，a＝15，b＝10，A＝60°，则cos B＝() A．－22 3 B. 22 3 C．－ 6 3 D. 6 3 答案 D 解析依题意得0° 解析 由正弦定理a sin A ＝b sin B ，得1sin A ＝3 sin B . 又∵B ＝2A ，∴1sin A ＝3sin2A ＝3 2sin A cos A . ∴cos A ＝3 2，∴∠A ＝30°，∴∠B ＝60°，∠C ＝90°. ∴c ＝12＋(3)2＝2. 5．(2013·陕西)设△ABC 的内角A ，B ，C 所对的边分别为a ，b ，c ，若b cos C ＋c cos B ＝a sin A ，则△ABC 的形状为( ) A ．锐角三角形 B ．直角三角形 C ．钝角三角形 D ．不确定 答案 B 解析 ∵b cos C ＋c cos B ＝a sin A ，由正弦定理，得sin B cos C ＋sin C cos B ＝sin 2A ，∴sin(B ＋C )＝sin 2A ，即sin A ＝sin 2A . 又∵sin A >0，∴sin A ＝1，∴A ＝π 2，故△ABC 为直角三角形． 6．在△ABC 中，角A 、B 、C 所对的边分别为a 、b 、c ，已知A ＝60°，a ＝3，b ＝1，则c 等于( ) A ．1 B ．2 C.3－1 D. 3 答案 B 7．已知△ABC 的面积为3 2，且b ＝2，c ＝3，则( ) A ．A ＝30° B ．A ＝60° C ．A ＝30°或150° D ．A ＝60°或120° 答案 D 8．已知三角形面积为1 4，外接圆面积为π，则这个三角形的三边 课时作业(三十二) Unit 2 Robots Ⅰ.用所给词的适当形式填空 1.The superstar showed up at the court，________(accompany) by his manager. 2.The young lady dressed________(elegant) when she went to work. 3.He was right in his________(assess) and wrong in his prediction. 4.He is an________child.He always________his parents and never________rules in school or laws in society.(obey) 5.Everyone knows she is a________girl who has a________for singing.(talent) 6.It________in his________that the country was in a messy________.(state) 7.To the________of the boss，his products could________the need of the customers.(satisfy) 8.The old blind man asked me to do him a________and find his________book.(favour) 9.It is reported that the lost boy________(not find)so far. 10.Having a trip abroad is certainly good for the old couple，but it remains________(see) whether they will enjoy it. 答案：1.accompanied 2.elegantly 3.assessment 4.obedient；obeys; disobeys 5.talented; talent 6.was stated; statement; state 7.satisfaction; satisfy 8.favour；favourite 9.hasn't been found 10.to be seen Ⅱ.完成句子 1.John__________________(极其渴望)to become a writer of the science fiction. 2.__________________(据宣布)the new library which is under construction would be opened to the public next year. 3.His father isn't__________________(支持)his thought while his mother always__________________(陪他去书店)． 4.Do your parents often__________________(打电话)to ask your recent progress？ 5.__________________(且不说费用多少)，do we actually need a second car？ 6.Owing to his hard work，his classmates all think John__________________(注定会成功)． 7.I'm about to__________________(转身)and see who he is but my phone rings. 8.Her only fear was that her little son would______________(让……一个人留下)in the world in case something happened to her. （新教材）高中生物必修二全册课后“练习与应用+复习与提高” 汇总（附答案） 第1章遗传因子的发现 第1节孟德尔的豌豆杂交实验(一) 【练习与应用】 一、概念检测 1.在孟德尔的一对相对性状的豌豆杂交实验中，B都表现为显性性状，F的自交后代却出现了性状分离。据此判断下列相关表述是否正确。 (1)隐性性状是指生物体不能表现出来的性状。(×) (2)纯合子的自交后代不会发生性状分离，杂合子的自交后代不会出现纯合子。(×) 2.人眼的虹膜有褐色的和蓝色的，褐色是由显性遗传因子控制的，蓝色是由隐性遗传因子控制的。已知一个蓝眼男人与-一个褐眼女人(这个女人的母亲是蓝眼)结婚，这对夫妇生下蓝眼孩子的可能性是(A) A.1/2 B. 1/4 C.1/8 D.1/6 3.观察羊的毛色遗传图解，据图回答问题。 (1)毛色的显性性状是白色，隐性性状是黑色 (2)白毛羊与白毛羊通过有性生殖产生的后代中出现了黑毛羊，这种现象在遗传学上称为性状分离。产生这种现象的原因是白毛羊为杂合子，杂合子自交时会出现性状分离。即雌雄白毛羊均可形成含有控制黑毛的遗传因子的配子，雌雄配子随机结合，会产生黑毛羊。 二、拓展应用 1.水稻的非糯性和糯性是一对相对性状，非糯性花粉中所含的淀粉为直链淀粉，遇碘变蓝黑色，而糯性花粉中所含的是支链淀粉，遇碘变橙红色。现在用纯种的非糯性水稻和纯种的糯性水稻杂交，取F?花粉加碘液染色，在显微镜下观察，半数花粉呈蓝黑色，半数呈橙红色。请回答下列问题。 (1)花粉出现这种比例的原因是什么? F?水稻细胞含有一个控制支链淀粉合成的遗传因子和一个控制直链淀粉合成的遗传因子。在F?形成配子时，两个遗传因子分离，分别进入不同的配子中，含支链淀粉遗传因子的配子合成支链淀粉，遇碘变橙红色;含直链淀粉遗传因子的配子合成直链淀粉，遇碘变蓝黑色，其比例为1:1。 (2)实验结果验证了什么? 分离定律。即在F?形成配子时，成对的遗传因子发生分离，分离后的遗传因子分别进入不同的配子中。 (3)如果让F?自交，F?中花粉有2种类型。 2.某农场养了一群马，马的毛色有栗色和白色两种。已知栗色和白色分别由遗传因子B 和b，控制。育种工作者从中选出一匹健壮的栗色公马，拟设计配种方案鉴定它是纯合子还是杂合子(就毛色而言)。请回答下列问题。 (1)在正常情况下，一匹母马一次只能生一匹小马。为了在个配种季节里完成这项鉴定，应该怎样配种? 将被鉴定的栗色公马与多匹白色母马配种，这样可在一个季节里产生多匹杂交后代。 (2)杂交后代可能出现哪些结果?如何根据结果判断栗色公马是纯合子还是杂合子? 杂交后代可能有两种结果:一是杂交后代全部为栗色马，此结果说明被鉴定的栗色公马很可能是纯合子;二是杂交后代中既有白色马，又有栗色马,此结果说明被鉴定的栗色公马为 高中数学学习材料 （灿若寒星 精心整理制作） 课时作业20 基本不等式 时间：45分钟 满分：100分 一、选择题(每小题5分，共35分) 1．a ＋b ≥2ab (a >0，b >0)中等号成立的条件是( ) A ．a ＝b B ．a ＝－b C ．a ＝|b | D ．|a |＝b 【答案】 A 【解析】 由基本不等式成立的条件易知． 2．x 2＋y 2＝4，则xy 的最大值是( ) A.12 B ．1 C ．2 D ．4 【答案】 C 【解析】 xy ≤x 2＋y 2 2＝2，当且仅当x ＝y ＝2或x ＝y ＝－2时，等号成立，∴xy 的最大值为2. 3．若a >b >1，P ＝lg a ·lg b ，Q ＝1 2(lg a ＋lg b )，R ＝lg a ＋b 2，则( ) A ．R C ．Q 高考英语一轮复习 Unit2 Robots课时作业 新人教版选修7
(新教材)高中生物必修二全册课后“练习与应用+复习与提高”汇总(附答案)
北师大版高中数学必修五课时作业20 基本不等式