新概念第二册lesson14：I had nearly reached the town ,when the young

新概念第二册lesson14：I had nearly reached the town ,when the young man suddenly said,very slowly,"Do you speak English?"中的when的用法…………多谢啦!

when 引导的时间状语从句
时间状语从句,由以下连词引导：
when while as after before as soon as since till /until by the time 在时间状语从句中,要注意时态一致.一般情况下主句是将来时的时候,从句要用一般现在时.
时间状语从句（adverbial clause of time）
1.由when,while,as引导的时间状语从句.例如：
When you think you know nothing,then you begin to know something.当你以为自己一无所知的时候,你就是在开始知道一些事物了.
When truth is buried under the ground it grows,it chokes,it gathers such an explosive force that on the day it bursts out ,it blows up everything with it.当真理被埋在地下的时候,它在生长,它感到压抑,它蓄存着这么一种爆炸性力量,一旦冒出,它就会炸破一切!
Strike while the iron is hot.趁热打铁.
Will you watch my clothes while I have a swim.我游泳的时候,请你照看一下我的衣服.
You can feel the air moving as your hand pushes through it.当你的手在空气中挥动的时候,你就能感觉到空气在流动.
Our headmaster laughed as she spoke.我们的校长边谈边笑.
when,while和as的区别
when引导的从句的谓语动词可以是延续性的动词,又可以是瞬时动词.并且when有时表示“就在那时”.
例如：
When she came in,I stopped eating.她进来时,我在吃饭.(瞬时动词)
When I lived in the countryside,I used to carry some water for him.当我住在农村时,我常常为他担水.（延续性的动词）
We were about to leave when he came in.我们就要离开,就在那时他进来了.
While引导的从句的谓语动作必须是延续性的,并强调主句和从句的动作同时发生（或者相对应）.并且while有时还可以表示对比.例如：
While my wife was reading the newspaper,I was watching TV.(was reading是延续性的动词,was reading和was watching同时发生)
I like playing football while you like playing basketball.我喜欢踢足球,而你喜欢打篮球.（对比）
As表示“一边……一边”,as引导的动作是延续性的动作,一般用于主句和从句动作同时发生；as也可以强调“一先一后.例如：
We always sing as we walk.我们总是边走边唱.（as表示“一边……一边”）
As we was going out,it began to snow.当我们出门时,开始下雪了.（as强调句中两个动作紧接着先后发生,而不强调开始下雪的特定时间）
as when while的辨析
as when while都表示主、从句动作同时发生,三者差异如下：
表示“一边.一边”的意思
as 强调两个动作同时进行,并表示对比时
用于发生时间较短时
when
1、还可以表示从句动词的动作在主几句动词的动作”之前 ”或”之后”发生.
2、when＝and then; at that moment (正在那个时候)
while 1、用于时间较长时
2、 强调两个动作同时进行,并表示对比时
有时这三个连词可以互换,有时不可以.
lIt was raining hard when (as) I got there.
我到那里时,正在下大雨.( 动作同时发生,when可换为as,但不能换为while,因为get是点动词.)
lWhen I had read the article,he called me.
我看完这篇文章之后,她给我打了电话.( 从句动作发生在主句之前,注意时态表达,只能用when )
lWhen I got to the cinema,the film had begun.
(当)我到了电影院时,电影已经开演了.(从句的动作发生在主句之后,只能用when,并要注意时态)
lHe was about to leave,when the telephone rang.
他正要离开,忽然电话响了.( 此时不能放在句首.主句动词一般表达 “正在” “即将”.
while,as不能代替
lShe thought I was talking about her daughter,while,in fact,I was talking about my daughter.
他以为我在谈她女儿,然而,实际上在谈论我女儿.(表转折,对比,when,as都不能代替它)
lWhile the alien was buying a souvenir,the girl called the police.
外星人买纪念品时,那女孩给警察打了电话.(表示主句,从句的动作同时发生,while后引导的状语从句的动词必须是延续动词不能是点动词,因为它表示较长时间)
lMother was worried because little Alice was ill,especially as (when/ while) father was away.
妈妈担心,因为小爱丽丝病了,特别是他父亲不在家的时候.(此时as ,when,while可通用)