as，when，while的区别是什么

when , as , while 这三个词都可以引出时间状语从句，它们的差别是：when 从句表示某时刻或一段时间 as 从句表示进展过程，while 只表示一段时间
When he left the house, I was sitting in the garden.

当他离开家时，我正在院子里坐着。

When he arrived home, it was just nine o'clock.

当他到家时，正是九点钟。

As he grew older, he became more intelligent.

随着他年龄的增长，他变得更有才智了。

While he was in London,he studied music.

当他在伦敦时，他学习音乐。

While she was typing the letter,the telephone rang.

当她在用打字机打那封信时，电话响了。

when, while这三个词都有"当……时候"之意，但用法有所不同，使用时要特别注意。

①when意为"在……时刻或时期"，它可兼指"时间点"与"时间段"，所引导的从句的动词既可以是终止性动词，也可是持续性动词。如：

When I got home, he was having supper.我到家时，他正在吃饭。

When I was young, I liked dancing.我年轻时喜欢跳舞。

②while只指"时间段"，不指"时间点"，从句的动词只限于持续性动词。如：

While I slept, a thief broke in.在我睡觉时,盗贼闯了进来。

辨析

①when从句与主句