时间状语从句
常用引导词：when, while, as, as soon as, before, after, till/until, since
1、when, while, as
（1）三者均可表示“当……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 while/when/as I was walking along the street．当我沿街散步时碰见了康丽。
Don’t make any noise while/when/as I am recording. 我录音时（你们）别发出声音。
（2）while
1）while只能与持续性动词连用，且常用进行时态。表示主句的行为在从句行为进行的过程中发生。如：
While they were crossing the Atlantic, many people died. 他们中的很多人在横渡大西洋时丧生了。
2）表示主句和从句的动作同时发生。如：
While the wife was cooking, the husband was watching TV. 妻子在做饭的时候，丈夫在看电视。
3）表示“然而”，主句和从句是两个对应的动作。如：
Lucy likes dancing while Lily likes doing sports. 露西喜欢跳舞而莉莉喜欢运动。
（3）when
1）when既可以和持续性动作连用，也可以和瞬间性动作连用，主句与从句描述的动作既可以同时发生，也可以先后发生。如：
When the weather is fine, many people go out for a walk. 天气好时，很多人都出去散步。
When I got home, I found my baby girl singing in the sitting room. 我到家时，发现我的小女儿正在客厅里唱歌。
2）表示“某人正在做某事，突然……”，主句用过去进行时，从句用一般过去时，表示一个动作正在进行的时候，另一个动作（突然）发生了，强调后一动作发生的突然性。如：
We were talking when the teacher came in. 我们正在讲话，老师（突然）进来了。
试比较：
While we were talking, the teacher came in. 我们正在讲话的时候，老师进来了。（不强调突然性。）
3）表示“某人正要做某事，就在这时……”，主句用过去将来时，从句用一般过去时。如：
I was leaving when somebody touched my shoulder. 我正要离开，就在此时有人碰了一下我
的肩膀。
（4）as
as与when用法相似，但着重强调主句动作与从句动作同时发生，有“随着……”或“一边……一边……”之意。如：
As you get older, you get more knowledge. 随着年龄的增长，你获得的知识就越多。
They sing as they walk. 他们一边走一边唱。
练习
（一）用when, while, as填空
1. I was looking out of the window ________ the teacher asked me.
2. What is he doing ________ his parents came back?
3. Mike was playing games ________ Jack was studying.
4. I was about to fall asleep ________ the baby began to cry.
5. ________ the children walked along the lake, they sang happily．
6. Someone stepped on my toes ________ I was waiting for the bus.
7. ________ she grew older, she became more responsible.
（二）单项选择
1. When I got to the factory, the workers _____ about the film.
A. are talking
B. talked
C. were talking
D. have talked
2. I _____ a letter when my mother came in.
A. write
B. am writing
C. was writing
D. have written
3. My mother _____ while my father _____ TV.
A. cooks; was watching
B. was cooking; was watching;
C. was cooked; watched
D. cooked; watched
4. They were sleeping _____ they heard a man _____ “help”.
A. when; shouting
B. while; to shout
C. when; to shout
D. while; shouting
2、as soon as
表示“一……就……”，强调动作紧密相连。如：
We began to work as soon as we got there. 我们一到那儿就开始工作了。
We always go somewhere interesting as soon as the holiday begins. 假期一开始，我们就会去某个好玩的地方。
I will write to you as soon as I arrive there. 我一到那里就会给你写信。（主将从现）
