1.意为“一……就……”,表示从句的动作一发生,主句的动作随即发生。
例:You'd better ring me up as soon as you get there.
你最好一到那里就给我打个电话。
2.主句用一般将来时或主句是祈使句时,从句需要用一般现在时表示将来。
例:Wu Yi will help the housework as soon as she gets home after school.
吴怡放学后一回家就帮忙做家务。
1.意为“自从……”,主句常用现在完成时,从句常用一般过去时。
例:My grandmother has seen a lot of changes in Tianjin since she came here.
自从奶奶来到天津,她看到了许多变化。
2.从句谓语动词是延续性动词或表状态的动词,则从句表示的时间从该动作或该状态结束时算起。
例:(1)It has been two years since he worked here.
他不在这里工作已经两年了。
(2)Tom has written to me regularly since he was ill.
自从病好以后,汤姆定期给我来信。
3.从句谓语动词是非延续性动词,则表示的时间从该动作开始的那一刻算起。
例:Joy has studied very hard since she came to our school.
自从Joy来到学校,她学习就非常努力。
4.It is/has been... since... 句式的用法:“It is/has been+时间段+since从句”意为“自从……以来有(多久)”,since从句不可用否定形式。
例:It is/has been 2 years since we last met.
自从我们上次见面已经有两年了。
1.主句为否定句时,常构成“not...until”句型,意为“直到……才”,主句谓语动词需用非延续性动词(表示主句的动作到从句表示的时间点才开始)。
例:Sandy didn't leave until/till I came back.
直到我回来Sandy才离开。
2.主句为肯定句,主句谓语动词需用延续性动词(表示主句的动作到从句表示的时间点才结束)。
例:I will wait until/till I hear from you.
我会一直等,直到收到你的来信。
备注:(1)强调结构中只能用until,不能用till。
例:It is not until 9:00 am that they begin their class every day.
他们每天早上九点才开始上课。
(2)位于句首时用until而不用till。
例:Until you told me, I heard nothing of what had happened.
直到你告诉我,我才知道发生了什么事。
1.before意为“在……之前”,表示主句动作发生在从句动作之前。
例:Don't forget to wash your hands before you have meals.
你吃饭之前不要忘了洗手。
2.after意为“在……之后”,表示主句动作发生在从句动作之后。
例:Jo arrived after the game started.
比赛开始后Jo才到。
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