When一词的用法
when，主要用作副词、连词、代词、名词，作副词时意为“什么时候；什么情况下；什么场合下；（用于时间的表达方式之后）在那时，其时；当时，当场”，作连词时意为“在……时候；在……之后；在任何……时候；一……就； 考虑到，既然；虽然，然而，可是”，作代词时意为“什么时候；何时”，作名词时意为“时间，时候；日期；场合”。
when一词的用法我相信大家并不陌生。我们看下2道高考题：
1、Today I was having a PE lesson while I fell down and hurt my foot.（07福建高考题短文改错）
2、I was about to answer him while I noticed that the last plate on my tray began to fall. （07辽宁高考题短文改错）
分析：
1、Today I was having a PE lesson when I fell down and hurt my foot.
2、 I was about to answer him when I noticed that the last plate on my tray began to fall.
这2个题都在考察when一词的用法。可能有些同学会产生疑问，为什么非when莫属呢？while怎么不对呢？
让我们谈谈它们的区别。
1、 While可以作为时间状语从句连词，译成"在……期间"，一般只和延续性动词连用。When作为时间状语从句的连词，没有这个限制，后面可以是延续性动词，也可以是暂短性动词，因此，一定程度上，when是能代替while的。
上面的改错题，从从句的动词上就可以看出while不对，因为fell与noticed都是暂短性动词，不与while连用。
2、 但在其余从句中，它们是截然不同的。在本题中，when译成"这时"，等于and then，是并列连词，而且专门与过去进行时连用，或者与be about to do连用。即：
1） ……was/were doing……when……did 正在做……这时……
2） ……was/were about to do……when……did 正要做……这时……
这个知识点是高考中常见的考点。大家可以做一下：
1. （2004上海卷）Jasmine was holidaying with her family in a wild life park ___ she was bitten on the leg by a lion.
A when B while C since D once
2. （2006辽宁卷）He was about halfway through his meal _____a familiar voice came to his ears.
A why B where C when D while
3. （2004北京春）We were swimming in the lake _____ suddenly the storm started.
A when B while C until D before
4. （2006湖南卷）I had just stepped out of the bathroom and was busily drying myself with a towel ____ I heard the steps.
A while B when C since D after
5. （2006安徽卷）I ____along the street looking for a place to park when the accident _____.
A went， was occurring B went， occurred C was going， occurred D was going， had occurred
答案：
1. A was holidaying……when…… 正在度假这时被咬
2. C was about ……when…… 正吃到一半这时听到熟悉的声音
3. A were swimming ……when…… 正在游泳这时暴雨
4. B was busily drying……when…… 正在擦干身体这时听到脚步声
5. C was going ……when…… 正在走着这时发生事故
