before和since引导的时间状语从句？

0榛 2023-03-20 17:54

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  0榛

  2023-03-20 18:19

  在并列句和状语从句这个专题中，考点大概有三个：一、状语从句的引导词与介词的用法比较;状语从句与定语从句引导词的辨析。二、同类状语从句中近似连接词的用法差异。三、whatever、whenever、wherever等引导词与no matter wh-等引导词的不同用法。在这里，我们就先来看看由before与since引导的时间状语从句有何区别。

  before与since引导的时间状语从句：

  1、如果表达“还未……就……;不到……就……;……才……;还没来得及……就……”时，需用连词before.

  例句：We hadn't run a mile before my sister felt tried.

  我们跑了还不到一英里我妹妹就感到累了。

  2、before从句中谓语不用否定式。

  Before they reached the station, the train had gone.

  他们还没有到火车站，火车就已经开走了。

  3、It will be + 一段时间+before…还要多久才……。

  例句：It will be a year before I come back.

  还得再过一年我才能回来。

  4、since 从句的谓语动词一般是非延续性动词，主句的谓语动词是延续性的或者是反复发生过的动作。since从句的时态若是一般过去时，相应地，主句中的时态是现在完成时或现在完成进行时。

  例句：I have written home three times since I came here.

  自从我来到这儿，我已经给家里写过三封信了。

  5、在“It is + 一段时间 +since 从句”句型中，其句意取决于从句的谓语动词是否可延续。

  例句：It is two years since the war broke out.

  自战争爆发以来有两年了

  1.Close the door before you leave the room. 离开房间前关上门。

  2.she worked in shsnghai before she came here.she had studied english for six years before she went to college.

  3.It has been almost five years since I taught high school students.我不教高中已经大概有五年了。

  since从句中的动词不同，其起算时间也不同。' since+瞬间动词过去时 ' 是从该动作发生时起算；' since+延续性动词过去时 ' 是从该动作结束时起算。试比较:

  　　He has worked very hard since he entered the factory.

  　　We haven't seen each other since I worked in the factory.

  　since常用于“It' a+some time+since sb. did sth“结构。试比较:

  　　It's two years since he joined the army.他参军有两年了。

  　　It' a two years since be was a soldier.他退役有两年了。

  before:　　

  before有时可译为“还没……就“。

  　　【例】He had measured me beforer I could say a word.

  我还没来得及说话, 他就给我量好了尺寸。

  　 　I hadn't waited long before he came.

  我还没等多久他就来了。

  before也可用于it结构，与 since 结构比较相似，注意它们所用时态的区别，其结构通常是:'It will be + some time +before sb. does sth.’或' It was + some time + before sb. did sth. '。可表示将来或过去两个概念。常译作“……才……”。
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