①while、when、as均可表示动作同时发生,但while、as后面必须接延续性动词或持续的状态。
例如:
1.He fell asleep while he was doing his homework.(从句动词用进行时表动作的延续)
2.I learned English while I was in England.(从句意思本身表示持续的意思)
3.The students took notes as they listened. (listen为延续性动词)
while译为“尽管”时,不引导时间状语从句。
②since表自从时,通常主句用现在完成时,since引导的从句用一般过去时。
例如:I have had two jobs since I graduated.
③until、till词义相同,但在肯定句和否定句中用法有区别。
A.肯定句中表示“直到...为止”,动词必须为延续性。
例如:I slept until midnight.我一直睡到半夜时醒了。
B.否定句中表示“直到...才...”,动词不受限。
例如:She didn’t arrive until 6 o’clock. 她直到6点才到。正确使用这两个连词的关键之一就在于判断句中的动词该用肯定式还是否定式。
④在短文填空中,when,before和until常常分不清楚,来看一看它们的区别。
When、until、before所强调的动作截止的时间点不同
例如:
She lived in the house until he came back.
她在那所房子里一直住到他回来。(强调“到此为止”)
She lived in the house before he came back.
在他回来之前,她一直住在那所房子里。(强调“在....之前”)
She lived in the house when he came back.
当他回来的时候,她住在那所房子里。(强调“当....时”)