when和while的用法区别。

具体你可以参考这一段。
when，while，as引导时间状语从句的区别
when，while，as显然都可以引导时间状语从句，但用法区别非常大。
一、when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。
① Why do you want a new job when youve got such a good one already？（get为短暂性动词）你已经找到如此好的工作，为何还想再找新的？
②Sorry，I was out when you called me．（call为短暂性动词）对不起，你打电话时我刚好外出了。
③Strike while the iron is hot．（is为延续性动词，表示一种持续的状态）趁热打铁。
④ The students took notes as they listened．（listen为延续性动词）学生们边听课边做笔记。
二、when从句的谓语动词可以在主句谓语动作之前、之后或同时发生；while和as从句的谓语动作必须是和主句谓语动作同时发生。
1．从句动作在主句动作前发生，只用 when。
①When he had finished his homework，he took a short rest．（finished先发生）当他完成作业后，他休息了一会儿。
②When I got to the airport，the guests had left．（got to后发生）当我赶到飞机场时，客人们已经离开了。
2．从句动作和主句动作同时发生，且从句动作为延续性动词时，when，while，as都可使用。
①When ／While ／As we were dancing，a stranger came in．（dance为延续性动词）当我们跳舞时，一位陌生人走了进来。
②When ／While ／As she was making a phonecall，I was writing a letter．（make为延续性动词）当她在打电话时，我正在写信。
3．当主句、从句动作同时进行，从句动作的时间概念淡化，而主要表示主句动作发生的背景或条件时，只能用 as。这时，as常表示“随着……”；“一边……，一边……”之意。
① As the time went on，the weather got worse．（as表示“随着……”之意）
② The atmosphere gets thinner and thinner as the height increases．随着高度的增加，大气越来越稀薄。
③As 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。
④The little girls sang as they went．小姑娘们一边走，一边唱。
⑤The sad mother sat on the roadside，shouting as she was crying．伤心的妈妈坐在路边，边哭边叫。
4．在将来时从句中，常用when，且从句须用一般时代替将来时。
①You shall borrow the book when I have finished reading it．在我读完这本书后，你可以借阅。
②When the manager comes here for a visit next week，Ill talk with him about this．下周，经理来这参观时，我会和他谈谈此事。
三、when用于表示“一……就……”的句型中（指过去的事情）。
sb．had hardly（＝scarcely） done sth．when．．．＝Hardly ／ Scarcely had sb．done sth．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。
②I had hardly ／scarcely entered my room when the telephone rang．＝Hardly ／Scarcely had I entered my room when the telephone rang．我刚一走进房门，电话就响了。
定语从句的关系代词 Which的用法: 若先行词指物则代替先行词在定语从句中充当主语或宾语.

This is the pen which was given by my friend.

先行词 指物代替先行词在定语从句中充当主语

This is the pen which my friend gave to me.

先行词 指物代替先行词在定语从句中充当宾语

下面是他和that在定语从句中的区别及用法：
that \which在代物时常常可以通用,但有时只宜于用which ,不用that

(1) 关系代词前有介词时.

This is the hotel in which you will stay.

(2) 如有两个定语从句,其中一句的关系代词是that,另一句宜于用which.

Let me show you the novel that I borrowed from the liberary which was newly open (新开放) to us.

注意2that \which在代物时常常可以通用,但有时只宜于用that ,不用which.

(1) 先行词是形容词最高级或者它的前面有形容词最高级时

This is the best that has been used against air pollution(反对空气污染) in cities.

English is the most difficult subject that you will learn during these years.

(2) 先行词是序数词,或它的前面有一个序数词时

He is the last person that I want to see.

(3) 主句中已有疑问词时

Which is the bike that you lost?

(4) 先行词既有人又有物时

The bike and its rider that had run over (撞倒了)an old man were taken to the police station.

(5) 先行词是all,much,little,something,everything,anything,nothing,none,the one等代词时

You should hand in all that you have.

We haven’t got much that we can offer you.

I mean the one that you talked about just now.

(6) 先行词前面有only,any,few,little,no,all,one of,the same,the very等词修饰时

The only thing that we can do is to give you some money.

Li Ming is the only one that got full marks (满分)in our class.

Li Ming is one of the students that want to be teachers in our class.

(7) 有两个定语从句,其中一个关系代词已用which,另外一个宜用that

Edison built up a factory(办了一个工厂) which produced things that had never been seen before.

定语从句的关系副词 Where的用法:若先行词指地点且其在定语从句中充当地点状语.

This is the house+I was born in the house. (=I was born there)

介词短语 副词

=This is the house where I was born.这就是我在那儿出生的房子.

先行词 关系副词

in which I was born.

介词+关系代词

which I was born in.

关系代词

这里作介宾的which和that可以省略

that I was born in

while 强调的是两个动作/事件的同时发生。
He was text messaging while he was driving. Thatś a very dangerous thing to do.

when 当。。时候， 强调从句里的事情发生的时候主句的一种状态。
I was still a kid when I read that book.
He was in the kitchen when the phone rang.
也可以用来表示在一件事情发生以后。 (
Give me a call when you finish your homework.