1．when, while和as的用法when “当……时候”，可与延续性动词或短暂性动词连用；从句动作可以发生在主句动作之前、之后或与主句动作同时发生 When you apply for a job, you must present your credentials. 当你申请工作时，你必须递交你的有关证件。 while “当……时候”，一般与延续性动词连用，从句动作与主句动作同时发生 Mary made coffee while her guests were finishing their meal. 客人们就要吃完的时候，玛丽去煮咖啡了。 as “一边……一边……”，常与延续性动词连用，从句动作与主句动作同时或几乎同时发生 As he grew older, he became less active. 随着他逐渐长大，他变得不那么活泼了。 如果主句表示的是短暂性动作，而从句用延续性动词的进行时表示在一段时间内正在进行的动作时，when, while与as可互换使用。 ◆When/While/As I was walking down the street, I came across an old friend of mine. 我正沿着大街走时，碰巧遇到了我的一个老朋友。 2．before与since的用法(1)before表示“在……之前；还未……就……；还没来得及……就……”。常用于句型“It will be/was＋时间段＋before从句”(在……之前还要多久，过了多久才……)。 ◆John thinks it won’t be long before he is ready for his new job. 约翰认为不久他就能为他的新工作做好准备。 (2)since表示“自从……以来”，常用于“It is/has been＋时间段＋since从句”结构。该句型表示“自从开始(不做)……已经多长时间了”，一般从句的时态用一般过去时，主句中的时态用现在完成时。 ◆As is reported, it is over 100 years since Tsinghua University was founded. 据报道，清华大学已经建立了100多年了。 3．not…until…表示“直到……才”，主句谓语动词必须是非延续性动词。◆As far as I know, his mother won’t go to bed until he returns home every evening. 据我所知，他母亲每晚直到他回家才会上床睡觉。 4．as soon as/hardly…when/no sooner…than/the moment/the instant/the second/immediately/directly/instantly: hardly…when和no sooner…than的意义相当于as soon as，但只表示过去发生的事情，主句为过去完成时，从句为过去时，hardly或no sooner位于句首时语气强，而且主句的谓语要用部分倒装。◆Just use this room for the time being, and we’ll offer you a larger one as soon as it becomes available. 暂时用这个房间，一有空的大房间我们就给你。 5．every time/each time/last time/next time/by the time：在时间状语从句中，不能用一般将来时或过去将来时，而要用一般现在时或一般过去时代替将来时。◆Next time you come here, I will tell you. 下次你来的时候，我将告诉你。 [典例] (全国卷Ⅰ)He even scared my classmates away during they came over to play or do homework with me. during→when 解析：during是介词，不能引导状语从句，when是连词，可以引导状语从句，从句中的动词既可以是短暂性动词也可以是延续性动词。此处需要表示时间的连词，所以用when。 |
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