1．时间状语从句通常用下列从属连词来引导：after, before, as, once, till, until, (ever) since, when, whenever, while, now (that), as long as, as soon as。如： Now (that) you’ve grown up, you must stop this childish behaviour. Whenever we met with difficulties, they came to help us. Come and see us whenever you have time. People do not know the value of health till they lose it.

2．有些词，如 immediately, directly, instantly等，当用于 as soon as 意义时，也可以引导时间状语从句，如： I got in touch with him immediately I received his letter. My sister came directly she got my message. The machine will start instantly you press the button. I’ll telephone you directly I hear the news. Will you look for it immediately you get there?