:英语动词时态用法的详解

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  但是瞬间动词的否定结构可以与表示一段时间的状语连用，说明某动作不发生的状态可以持续一段时间
  e.g. She often goes on business. But she hasn’t left Shenyang for a month./since a month ago.
  过去进行时?
  过去进行时由was/were加现在分词构成，表示过去某个时刻或某一阶段正在进行的动作。常与表示过去某一时间的状语或when引导的谓语动词是一般过去时的时间状语从句连用。如：
  What were you doing at this time yesterday??
  My mother was cooking when I got home. ?
  过去将来时?
  过去将来时由should/would加动词原形或was/were going to加动词原形构成，表示
  从过去某时看来将要发生的事情，常用在宾语从句中。如：?
  I didn't know when he would come back. ?
  过去完成时?
  过去完成时由had加过去分词构成，表示过去某一动作或时间以前已发生或完成的动作，也可指从过去某时开始到过去另一时为止的动作或状态，即“过去的过去”。常用的时间状语有：a. by last month, by the end of last term等；b. before he came here, when I got there等。如：?

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