时间状语从句：

引导时间状语从句的从属连词有when(当……时候)，while(当，在……过程中)，since(自从……以来)，before(在……之前)，after(在……之后)，tell/until(直到……时)，as soon as(一……就)。如果主句为一般将来时，则时间状语从句只能用一般现在时表示将来的意义。

He was reading the newspaper when I came in.当我进来时，他正在读报纸。

Keep an eye on my cat while I am away.我不在时，请照看一下我的猫。

Don’t talk so loud while others are studying.别人学习时不要大声说话。

It has been five years since she went abroad.她出国已有五年了。

He died before his son came back.他在他儿子回来之前就去世了。

I’ll show him around our factory as soon as he arrives.他一到达我就领他参观我们的工厂。

I’ll tell him about it as soon as I see him. 我一见到他就告诉他。