when 有三个意思,分别如下:

(1) when做“当…时候”讲时,既可以引导瞬间动作,也可以引导延续性动作的词,如:

When I came into the room, he was writing a letter.
当我进屋时,他正在写信。

(2) when做“这时”讲时,通常用在如下句型中:
be doing\be about to do\be on the point to do…….when……(后半部分通常是一般过去时),意为某人刚要……这时……,此句型经常在考试中出现,同学们务必引起重视,特别是这个句型可以当成一个公式使用,题目给出任意两部分,都能确定另一部分的答案,如题目给了be doing和后面一个一般过去时的句子,中间连接词一定是when,或给了when和一般过去时的句子,前面一定是be doing\be about to do等。例:

I was walking along the street when suddenly someone patted me on the shoulder from behind.
我正在街上走着,这时忽然有人从后面拍我的肩膀。
又如:
I __B__ toward the door to go outside when suddenly Jim opened it unexpectedly.
A.walked B.was walking C.had walked D.had been walking
答案很显然为B teacheray.com

(3)when做“既然”讲,如:

Why do some rich people steal things __D__ they could easily afford to buy them?
A.unless B.before C.if D. when
意为既然富人能够很轻松地支付这些东西,为什么还要偷呢?
while 同样也有三个意思,分别如下:

(1)while也可作为“当…时候”讲,但while引导的动作必须是延续性的。

While it was raining, they went out.
天下雨的时候,他们出去了。

(2)while做“然而”讲,表示转折,通常有对比含义

All of us are working hard while he is sleeping.
所有人都在努力工作,然而他却在睡觉。

(3) while做“尽管”讲
While the numbers of such developments are relatively small, the potential market is large.
尽管这个项目发展的数量还比较有限,但它的潜在市场是巨大的。

此外when作为关系副词还可以引导定语从句做时间状语,而while不能引导定语从句,以上就是when和while所有的区别,我们在平常大大小小的考试中会经常遇到,不同情况下使用不同的引导词,同学们务必对这两个密切相关的词透彻理解,着重练习。

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