现在完成时
1,说明
现在完成时表示动作发生在过去,但与现在有关系,即用一个发生在过去的动作来说明现在的情况.
2,基本用法
（1）表示发生在过去并已完成但对现在还有影响的事情或经验,可与下列状语连用：already,yet,before,just,ever,never等.
I have already posted the photos.
Have you ever visited China?
（2）表示过去已经开始持续到现在的动作或过去某一时刻延续到现在包括现在在内的一段时间的状语连用.
I haven't seen her these days.
由since引导的时间状语.
They have lived here since 1989.
由for引导的时间状语.
I have known her for three years.
与表示包括现在时间在内的一段时间状语连用.
Have you returned the book today?
表示过去发生过的一次或多次情况.
Has the postman come yet?
He has never had breakfast.
过去完成时：
1,说明
过去完成时表示在过去某一段时间或动作以前已经完成的动作.由had+过去分词构成.
2,基本用法
表示在过去某一段时间或动作之前已经发生或完成的动作,动作发生的时间是“过去的过去”.
I had arrived home by that time.
He had left his case on the 4:30 train.
表示从过去某一时间开始持续到过去另一时间.
Great changes had taken place when he returned to his home town.
She had lived in a school for sixty years.
表示过去未曾实现的意图,打算,愿望等.常用于下列动词：
hope,think,plan,mean,expect,suppose,want等.
I had thought that my first teacher was dead.
I had hoped to attend the meeting.
在虚拟语气中,用以表示与过去事实相反的情况.
I wish that I hadn't spent so much money.
If he had followed my advice,he would have succeeded.
过去完成时常于下列状语连用：
already,yet,still,ever以及由by,before,when等引导的短语或从句.
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