when, while 和as ,until，assoon as(略)，before（略），after（略），since（略）引导时间状语从句的用法
定义：用表示时间的连词连接一个句子作状语就是时间状语从句。
连接词：when, while, as ,until
一、when 从句多用一般过去时，主句的时态视情况而定。
1. When he was a child he was alwaystrying out new ideas.
他小时候就常常试验一些新的设想。
2. When she came into my room, I was just reading a book.
她走进我房间时，我正在看书。
3. Sorry, I was out when you called me.
对不起，你打电话来的时候我出去了。
when 多用一般过去时，它表示的是一个时间点.when 从句的动词大多是瞬时动词。
温馨提示：（主将从现原则）
When the manager comes here for a visit
next week, I’ll talk with him about this.
下周，经理来这参观时，我会和他谈谈此事。
二、while 的用法
while 从句一般用的是进行时。主句根据具体情况而定。
1. While my wife was reading the newspaper, I was watching TV.
当妻子正在看报纸的时候，我正在看电视。
2. While Jim was mending his bike, Lin Tao came to see him.
正当吉姆修自行车时，林涛来看他。
3. While they were talking, the bell rang.
正在他们谈话的时候，上课铃响了。
4. You can’t do your homework while you’re watching TV.
你不能一边看电视一边做家庭作业。5. Strike while the iron is hot. 趁热打铁。这句话中，是说趁着铁是热的这段时间，赶紧打铁。如果换成 when 意思就变了，相当于说铁只热了一下，打一下，然后铁就冷了。这显然不符合文意。
三、as 的用法一般用一般过去时。as 从句一般可以翻译成“一边……一边……”。例如：
1. As my mother sang those old songs, tears ran down her cheeks.
当我妈妈唱起那些老歌时，眼泪顺着她的脸颊流了下来。
2. The students took notes as they listened. 学生们边听课边做笔记。3. As we talked on, he got more and more excited.
我们继续往下谈的时候，他越来越兴奋。
4. The little girls sang as they went.
小姑娘们一边走，一边唱。
as 常常翻译成“随着……”之意。
1. As the time went on，the weather got worse.
随着时间的推移，气候更加糟糕。
2. As years go by，China is getting stronger and richer.
随着时间一年一年过去，中国变得越来越富强了。
3.当从句的动作发生于主句动作之前，只能用when
When you have finished your work, you may have a rest.
干完活后，你可以休息一下。
4.从句表示随时间推移连词只能用as，不用when 或while。
As the day went on, the weather got worse.
日子一天天过去，天气越变越坏。
五、比较until（直到…为止）和not…until(直到…才)
Islept until midnight.
Ididn’t sleep until midnight.
Don"t get off the bus until it has stopped. 公共汽车停稳后再下车。
I didn"t manage to do it until you had explained how. 直到你教我后，我才会做。区别：until可用于句首，而till通常不用于句首。
Until you told me, I had heard nothing of what happened.
直到你告诉我以前，出了什么事我一点也不知道。
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