英语!大家知道现在完成时和过去完成时的区别吗?大家知道什么时候用现在完成时?什么时候用过去完成时吗?

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一、从结构上区别
现在完成时：主语 + have / has + 过去分词 （肯定式）
主语 + have / has + not + 过去分词 （否定式）
Have / Has + 主语 + 过去分词 （疑问式）
过去完成时：主语 + had + 过去分词 （肯定式）
主语 +had + not + 过去分词 （否定式）
Had + 主语 + 过去分词 （疑问式）
(二)从时间状语区别
现在完成时:常用的时间状语包括 “now,today,tonight,this week,this year,already,yet,just,recently…etc”.
过去完成时:常用的时间状语包括 “by,at,before等构成的短语”.
注意：当表示一段时间,现在完成时和过去完成时都可以用for 或since引导的状语.
例如：Have you had your lunch yet?你吃午饭了吗?
Yes,I have .I’ve just had it.是的,我刚吃完.
I have had a clock now.我现在有一个闹钟了.
Have you already posted the photos?你把照片寄走了吗?
The meeting had begun when we got there.我们到那儿时,会议已经开始了.
We had learned about 5000English words by the end of last term.
到上学期末我们已经学了5000个英语单词.
They had done the work at five o’clock.在五点钟的时候他们已经完成了那项工作.
I’ve known Li Lei for three years.我认识李蕾已经三年了.
I have worked here since ten years ago.自从十年前我就在这工作.
We had not heard from him since we left here.自从我们离开以来一直没有收到他的来信.
They had then been without sleep for twenty-four hours.这时他们已经有24个小时没有合眼了.
(三)使用时注意事项
使用现在完成时应该注意：
1.“ have/ has got ”形式上是一种完成时,但和have/ has 为同一意义,即 “有”.
例如：Have you got a pen-friend?你有笔友吗?
Yes,I have.是的,我有.
Has he got a lot of work to do?他有许多工作要做吗?
No,he hasn’t.不,他没有.
2.have/ has gone to 与 have/has been to 的区别
have/ has gone to 强调“去而未归”； have/ has been to 强调“去而归还”.have/ has
been to常和once,twice,never,ever连用； have/ has gone to则不可.例如：
— Have Jack ever been to Beijing?杰克去过北京吗?
— Yes,he’s been there several times.是的,他去过好几次了.
— Where have Mary and Tom gone?玛丽和汤姆去哪里了?
— They’ve gone to London.他们去伦敦了.
3.非延续性动词不能用于“现在完成时 + 表示一段时间的状语”的句型中.
这类动词有：e,go,start,leave,die,buy,finish,join,borrow,stop等.但它们能够
用表示持续状态的相应的延续性动词替换句中的终止性动词.例如：
arrive,e → be here,be in
begin,start → be on
buy → havedie → be deadfall asleep(ill) → be asleep (ill)finish,end → be overget to know → knowget up → be u