1、用作从属连词,意为“当……的时候”,引导时间状语从句。例如:
They learned a lot from the peasants when they stayed in the village.
他们住在那个村子时,从农民那里学到了许多东西。
It was snowing when he arrived at the station.他到达车站时,天正下着雪。
注意:如果 when 引导的从句中的主语和主句中的主语一致,且从句中的谓语动词是“ be +分词”或从句主语是 it ,则 be 动词及其主语常可省略。例如:
When( he was ) asked why he was late,he made no answer.当被问到他为什么迟到时,他避而不答。
I'll tell him about it when ( it is ) possible.在可能的时候,我会把那件事告诉他的。
2、用作从属连词,意为“一……就……”,引导时间状语从句。例如:
We will stand up when the teacher comes into the classroom.老师一进教室我们就起立。
Fire the rockets when I give the signal.我一发信号,你就点燃火箭。
3、用作从属连词,意为“还没 / 刚刚……就”,引导时间状语从句。例如:
I had hardly opened the door when he came in.我刚一开门,他就进来了。
I had not been reading for half an hour when I heard someone call my name.我刚刚看了半个小时的书,就听到有人叫我的名字。
用作从属连词,意为“倘若,如果”,表示条件。