否定句 用短暂性动词 意为"直到......才......"，表示主句中的动作到从句动作发生时开始 　　He waited until she had finished speaking.

　　他一直等到她讲完。

　　You can't go home until you finish your work.

　　工作完成后你才能回家。

　　[名师点津]

　　(1)till和until一般情况下两者可以互换，但till不可用于句首并且在强调句中多用until。

　　(2)如果将"not until ..."结构放在句首，那么主句要部分倒装。

　　It was not until the meeting was over that he began to tell me the secret.

　　直到会议结束他才开始告诉我那个秘密。

　　Not until we pointed out their fault to them did they realize it.

　　直到我们向他们指出了他们的错误，他们才意识到。

　　3．由since引导的时间状语从句

　　(1)若since引导的状语从句的谓语动词是非延续性动词的过去时，则从句表示的时间是"从动作开始的那一时刻起"。

　　We have been missing them since they left here.

　　自从他们离开这儿以来我们一直想念他们。

　　(2)若since引导的状语从句的谓语动词是延续性动词或表示状态的动词的过去时，则从句表示的时间是"从那延续性动作或状态结束时算起"。

　　How long is it since you lived in Shanghai?

　　你多久不住在上海了？

　　4．由before引导的时间状语从句

　　(1)before 意为"在......之前"，置于主句前后均可。

　　Before the sun sets, we must go home.

　　太阳落山前，我们必须回家。

　　(2)如果before引导的从句位于主句之后，有时不能译成"在......之前"，而要译成"过了多久就......""还未......就......"等

The struggle lasted four years before the North won in the end.