九大状语从句总复习
状语从句在主从复合句中修饰主句中的动词、形容词或副词等，按意义可以分为时间、地点、原因、目的、结果、条件、方式、比较、让步等状语从句。
一．时间状语从句。
通常由从属连词when, whenever, as, while, before, after, as soon as, till, until, since, once (一旦), hardly……when…, no sooner…….than…;等引导。例如：
The cyclist started just as the lights changed to green.
Whenever we met with difficulties , they cam to help us.
He didn’t leave his office until he had finished the day’s work.
应注意的问题
1．在时间状语从句中，通常要用动词的一般现在时态表示一般将来时态，用一般过去时态表示过去将来时态。但when引导一般疑问句或名词性从句时不受上述语法规则的限制，因此，应该加以区分。例如：
When China will enter WTO depends on the bilateral (双边的)joint efforts.
Once you understand the rules of the game, you’ll enjoy it.
2.when , while, as的不同用法。一般说来，当主、从句的动作是同时发生的事，三者可以换用。when既可以引导一个持续动作，也可以引导一个短暂动作，可用于主句和从句动作同时发生或从句动作先于主句动作；while引导的动作必须是持续性的，强调主句和从句的动作同时发生，往往侧重主句和从句动作的对比；as用于引导“在某行为的继续中发生某事”的“继续之行为”，所以多与过去进行时连用，翻译成“一边……一边……”或者表示动作的变化，翻译成“随着……”。
例如：
I hope you’ll think of my words as/when/while you drive on the busy roads.
When he realized it, the chance had been lost.
When he came home, I was cooking dinner.
I was fat when I was a child.
He took a bath while I was preparing dinner.
As I was walking down the street, an American asked me for the directions to the nearest station.
He sang songs as he was taking a bath.
As he gets older he gets more optimistic.
另外还必须注意when和while的特殊用法。when可以表示“就在这时，突然”之意；而while则可以表示对比的含义，常可译作“而”。例如：
She thought I was talking about her daughter, ____, in fact, I was talking about my daughter.(NMET95)
A. whom B. where C. which D. while
答案：D.本句的意思是“她认为我在谈论她女儿，然而，实际上，我在谈论我女儿。”
再如：
I was about to go to bed when the phone rang a second time.
我正准备去睡觉，就在这时电话铃又响了。
3．since和before的用法区别。两者都可用于“It be since/ before-从句”的句型，区别在于since表示“自从……以来”，所在主、从句的谓语动词的时态关系是：It is/has been some time since sb did something.而before的含义则是“（过了多久）才……”,主、从句的时态关系是：It was/ had been some time before sb did sth。表示过去和将来时，两者相应的句型分别是：It was some time since sb had done something.和It will be some time before sb does something.例如：
It was / had been years before I came back from abroad.
It will be five years before we meet again.
4.一些表示时间的名词词组如：the first time, the second time, last time，the moment, the minute，the year, every time, each time , next time,或副词immediately, instantly, directly等也可以引导时间状语从句。例如：
I’ll tell you about it the moment you come.
I recognized her the minute I saw her.
I’m going to see him next time he comes to Shanghai.
He left Europe the year World War II broke out.
I got in touch with him immediately I received his letter.
My sister came directly( = as soon as ) she got my message.
5.till和until
till和until意义相同，多数情况下可以换用，但用以强调，句首多用until;在强调结构或与not连用时多用until.例如：
Nothing can be done till/until the boss returns.
We waited till/until they came back.
Until we know the facts, we can’t do anything about it.
Not until midnight did the noise of the street stop.
6.hardly……when和no sooner……than相当于as soon as之意，也可引导时间状语从句。从句谓语动词用一般过去时，主句谓语动词用过去完成时。hardly及no sooner置于句首时，语气较强，主句的谓语要部分倒装。例如：
We had hardly begun when we were told to stop.
= Hardly had we begun when we were told to stop.
The spy had no sooner returned home than he was told to go to another country.
= No sooner had the spy returned home than he was told to go to another country.
二．地点状语从句。
