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have或has是助动词，has用于第三人称单数，其它人称一律用have。
疑问句
现在完成时的一般疑问句式是把助动词have或has提到主语之前。
回答：Yes, … have(has).
No, … haven’t(hasn’t).
否定句：
现在完成时的否定句式是“haven't(hasn't)+过去分词”。
3. 现在完成时的时间状语:already, just, yet, since, ever, never;
4. 与一般过去时的区别：一般过去时是强调动作在过去发生，而现在完成时是强调过去发生的动作对 现在造成了影响和后果。
5.一般过去时的时间状语：yesterday, just now, …ago, last week, 2 years ago,in 1980等。
例：
We planted (plant) some flowers in the garden last week.
I have sent (send) the letter.
He has come (come ) back home, he is watching (watch) TV now.
David finished (finish) his homework just now.
The monkeys are full, because we have fed (feed) them.
A: I have lost (lose) my purse!
B. Bad luck! When did you lose (lose) it?
A: I lost (lose) it last night.
与现在完成时连用的几个副词：already, just, ever, yet, never
肯定句: already, just
疑问句和否定句: ever, yet, never
yet 常置于句末
already, never, ever just一般置于助动词have/has之后，过去分词之前.
例：用 already, just或never, yet完成句子
1) I have been to many big cities, but I have never been to Shanghai.
2) Most of us have already finished our compositions.
3) Have they taken down the old pictures yet ? No, not yet .
4) He has already visited Beijing twice.
5) I have just heard the news. I know it.
7. 现在完成时中的for和since
(1)for + 一段时间(用How long提问)
We have known each other for ten years. 我们相识10年了。
(2)since + 句子/具体时间
since 引导的短语或从句用How long提问
①since+过去一个时间点(具体的年、月、日、钟点等)。
Tom has eaten nothing since yesterday.
②since + 一段时间+ago
We have been friends since five months ago. 从5个月前起，我们就成了朋友。
③since+从句，表示“自过去某个时间、某件事情以来”，从句时态：一般过去时。
I have lived here since I left Shanghai.
④It is+一段时间+since从句，表示“自从某件事发生已有一段时间了”。
It is two years since I left school.
8. 在含for或since引导的时间状语的现在完成时中，谓语动词只能用延续性动词。非延续性动词不能直接和for或since 连用。
leave --- be away die --- be dead
begin/start --- be on finish --- be over
come here --- be here go there --- be there
come back --- be back fall asleep --- be asleep
get to/ arrive/reach --- be (in) leave --- be away from
go (get) out --- be out open sth --- keep sth open
join --- be in+组织机构/be a member of+组织机构
fall ill --- be ill get up --- be up
catch a cold --- have a cold borrow --- keep
buy --- have get to know --- know
put on---wear
例：
1. The old man died 4 years ago.
The old man has been dead for 4 years.
2. It is 4 years since the old man died.
Four years has passed since the old man died.
3. He joined the Party 2 years ago.
He has been in the Party for 2 years.
4. I bought the book 5 days ago.
I have had the book for 5 days.
