while\ as \when有何区别

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 从句表示某时刻两件事同时发生或同时发生一段时间，as 从句表示（某件事或某种状态）进展过程，while 只表示(两个动作同时进行)一段时间。（一般同时进行一段时间常用while连接）
例句：
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。