when所引导从句既可是延续性的,也可是终止性的.While 所引导的从句,动词只能是延续性的.
He was doing his homework,when the telephone rang.
The telephone rang while he was taking a bath.
I’ll phone you again when I get home.
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对比用while.持续动作,此时从句时态通常相同.
Would you look after the children while I do the shopping?
While I was playing the piano,my sister was doing her homework.不是什么时态都可以。要符合以上的中文。when的主要用法：1. 主将从现 I will tell him the news when he comes back.2. 表突然 I was doing my homework when the phone rang.3. 其他都是正常用法。while在中学阶段要记住前后动作同时进行。基本上都是现在或过去进行时。如果你是高中，还需掌握while表示虽然和然而的意思。