状语从句中的when, while和as的用法
一．when，while，as在时间状语从句中的区别：
①三者均可表示“当……的时候”，如果主句表示的是短暂的动作，而从句表示的是一段时间，三者可通用。如：
I met Kang Li as／when／while I was walking along the street．
当我沿街散步时碰见了康丽。
②when可以和延续性动词连用，也可以和短暂性动词连用；而while和as只能和延续性动词连用。如：
It was snowing when we got to the airport．当我们到达机场时，天正下着雪。
（不能用while）
③as强调主句与从句表示的动作同时发生，as常表示“随着……”；“一边……，
一边……；while强调主句表示的动作持续于while所指的整个时间内；when 可指主、从句所述动作同时或先后发生。如：
As the time went on，the weather got worse．（as表示“随着……”之意）
He sang as he went along．他边走边唱。
Please write while I read．我读的时候，请写下来。
When he reached home，he had a little rest．回到家后，他休息了一会儿。
④when用于表示“一……就……”的句型中（指过去的事情）。
somebody had hardly（＝scarcely）done …when．．．
＝Hardly ／Scarcely had somebody done …when．．．
①I had hardly ／scarcely closed my eyes when someone knocked at the door．
＝Hardly ／Scarcely had I closed my eyes when someone knocked at the door．我刚一闭上眼，就有人在敲门了。
二.when, while和as都可引导让步状语从句：
①when引导让步状语从句，意为“尽管，虽然”相当于though或although: They stopped trying when they might have succeeded next time.
②while引导让步状语从句，相当于although ，是较为正式的书面语:
While I am willing to go, I would like it better that you went.
③as引导让步状语从句必须倒装，从句中的表语，状语或动词原形置于句首，若表语为名词，前置时省略冠词。
Child as he is, he knows a lot.
Much as I like it, I will not buy it, for it’s too expensive.
Try as he might, he could n’t find a job.
三.when和while可用作并列连词:
①when作并列连词，意为“突然，正在那个时候”常运用于以下句型中：Somebody be about to do…when…
Somebody be on the point of doing…when…
Somebody be doing… when…
Somebody had done…when…
We were having a meeting when someone broke in.
We were about to set off on our way, when it suddenly began to rain.
②while作并列连词，意为“而，却”，表示对比。
He likes pop music, while I am fond of music.
四.when和as用于原因状语从句中:
①when=since, now that… “既然”
Why do you want a new job when you’ve got such a good one already?
②as意为“因为”，指说话双方都知道的原因。
As he was not ready in time, we went without him.
组题练习：
1. Success came ______ she began to play leading parts in radio plays.
A. While
B. as
C. when
D. if
2. The atmosphere gets thinner and thinner _______ the height increases.
A. When
B. as
C. while
D. since
3. I was just about to go to sleep______ there was a loud knock on the door.
A. While
B. when
C. as
D. since
4. They were surprised that a child should work out the problem_____ they themselves
couldn’t.
A. When
B. where
C. until
D. while
5. We were swimming in the lake______ suddenly the storm started.
A. When
B. while
C. until
D. before
6. I do every single bit of housework_____ my husband Bob just does the dishes now and then.
A. Since
B. while
C. when
D. as
7. _____ I accept that he is not perfect, I do actually like the person.
A. While
B. Since
C. Before
D. Unless
