this用在什么句子里

完成时态完成时态有两种用法：第一

现在完成时 （1）现在完成时用来表示对目前状况仍有影响的，刚刚完成的动作（常与yet，already，just连用），或者过去某一时刻发生的，持续到现在的情况（常与for，since连用）。 例如： 1）I have just finished my homework。 2）Mary has been ill for three days。 （2）常与现在完成时连用的时间状语有：since, for, during, over等引导出的短语；副词already, yet, just, ever, now, before, often, lately, recently等；状语词组this...全部

  现在完成时 （1）现在完成时用来表示对目前状况仍有影响的，刚刚完成的动作（常与yet，already，just连用），或者过去某一时刻发生的，持续到现在的情况（常与for，since连用）。
  例如： 1）I have just finished my homework。 2）Mary has been ill for three days。 （2）常与现在完成时连用的时间状语有：since, for, during, over等引导出的短语；副词already, yet, just, ever, now, before, often, lately, recently等；状语词组this week (morning, month, year), so far, up to now, many times, up to the present等。
  例如： 1）I haven’t been there for five years。 2）So far, she hasn’t enjoyed the summer vacation。
   3）There have been a lot of changes since 1978。 （3）完成时态可用在下列结构中： This (That) is (was) the first (second…) time +定语从句；This (That, It) is (was) the only (last) + n +定语从句；This (That, It) is (was) +形容词最高级+ n +定语从句。
  如果主句的谓语动词是一般现在时，从句的谓语动词通常用现在完成时；如果主句谓语动词是一般过去时，从句谓语动词通常用过去完成时。例如： （1）This is one of the rarest questions that have ever been raised at such a meeting。
   （2）There was a knock at the door。 That was the second time someone had interrupted me that evening。
   过去完成时 （1）表示过去某时间前已经发生的动作或情况，这个过去的时间可以用by，before等介词短语或一个时间状语从句来表示；或者表示一个动作在另一个过去动作之前已经完成。例如： 1）We had just had our breakfast when Tom came in。
   2）By the end of last year they had turned out 5, 000 bicycles。 （2）动词expect, hope, mean, intend, plan, suppose, wish, want, desire等用过去完成时，表示过去的希望、预期、意图或愿望等没有实现。
  例如： I had meant to take a good holiday this year, but I wasn’t able to get away。 另外两种表示“过去想做而未做的事”的表达方式是： 1）was / were + to have done sth, 例如： We were to have come yesterday, but we couldn’t。
   2）intended (expected, hope, meant, planned, supposed, wished, wanted, desired) + to have done sth, 例如： I meant to have told you about it, but I forgot to do so。
   （3）过去完成时常用于以下固定句型： 1）hardly, scarcely, barely + 过去完成时+ when + 过去时。例如： Hardly had I got on the bus when it started to move。
   2）no sooner +过去完成时+ than +过去时。例如： No sooner had I gone out than he came to see me。 3）by (the end of ) +过去时间，主句中谓语动词用过去完成时。
  例如： The experiment had been finished by 4 o’clock yesterday afternoon。 将来完成时 将来完成时表示在将来某一时刻将完成或在另一个未来的动作发生之前已经完成的动作；也可以用来表示一种猜测。
  常与将来完成时连用的时间状语有：by (the time / the end of ) + 表示将来时间的短语和句子；before (the end of ) + 表示将来时间的词语或句子；when, after等加上表示将来动作的句子等。
  例如： 1）By this time tomorrow you will have arrived in Shanghai。 2）I shall have finished this composition before 9 o’clock。
   3）When we get on the railway station, the train will probably have left。 完成进行时 完成进行时是完成时的强调形式，有现在完成进行时，过去完成进行时，将来完成进行时。
   （1）现在完成进行时表示过去某一时刻之前开始的动作或状态一直延续到过去某一时刻。例如： I have been looking for my lost book for three days, but I still haven’t found it。
   有少数动词如work, study, live, teach 等, 用现在完成时和现在完成进行时意思相差无几。 How long have you studied here? How long have you been studying here? 但就大多数动词而言,在不用表示一段时间地状语的情况下,现在完成时表示动作的完成,而现在完成进行时表示动作的继续。
   They have widened the road。 They have been widening the road。 （2）过去完成进行时表示过去某一时刻之前开始的动作或状态一直延续到过去某一时刻。
  例如： It had been raining cats and dogs for over a week and the downpour had caused landslides in many places。
   （3）将来完成进行时表示在将来某一时刻之前开始的一个动作或状态一直延续到将来某一时刻。例如： By the time you arrive tonight, she will have been typing for hours。
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