最新一般现在时的特殊用法

一般现在时的特殊用法

①时间状语从句，条件句中，从句用一般现在时代替将来时

When, while, before, after, till, once, as soon as, so long as, by the time, if, in case (that), unless, even if, whether, the moment, the minute, the day, the year, immediately

He is going to visit her aunt the day he arrives in Beijing. 他一到北京，就去看他姨妈。

典型例题

(1) He said he ________me a present unless I_______ in doing the experiment.

A. had not given; had not succeeded

B. would not give; succeed

C. will not give; succeed

D. would not give; will succeed.

答案B. 在时间，条件或让步主语从句中一般不用将来时。本题有He said，故为过去式。主句用将来时，故选B. 此处用一般过去式代替了过去将来时。

(2) 表示现在已安排好的未来事项，行程等活动。

The museum opens at ten tomorrow.博物馆明天10点开门。(实际上每天如此。)

②用一般现在时代替过去时

1 )“书上说”，“报纸上说”等。

The newspaper says that it's going to be cold tomorrow.

报纸上说明天会很冷的。

2) 叙述往事，使其生动。

Napoleon’s army now advances and the great battle begins.

现在拿破仑的军队大举进攻，战斗马上要打响了。

③用一般现在时代替完成时

1)有些动词用其一般现在时可代替完成时：

2)hear, tell, learn, write , understand, forget, know, find , say,remember.

3)I hear (= have heard) he will go to London.

4)I forget (=have forgotten) how old he is.

5)2) 句型“It is … since…”代替“It has been … since …”

6)3) It is (= has been) five years since we last met.

④有些动词用其一般现在时可代替现在进行时

1) 句型：Here comes… ；There goes…

Look, here comes Mr. Li.

快看，李先生来了。

Be careful! Here comes the bus.

当心，汽车进站了。人教版选修5化学第三章第二节醛练习知识点

第二节醛

知识点一醛类

1．醛的结构

(1)概念：由烃基或氢原子与醛基相连而构成的化合物。

(2)官能团：醛基(—CHO或)。

2．醛的分类

3．甲醛和乙醛

物质甲醛(蚁醛) 乙醛

分子式CH2O C2H4O

结构简式HCHO CH3CHO

物理性质颜色无色无色

气味有刺激性气味有刺激性气味

状态气态液态

溶解

性

易溶于水，35%～40%的甲醛水溶

液又称福尔马林

能跟水、乙醇等互溶

(1)概念：羰基与两个烃基相连的化合物。