现在完成时
（1）构成：现在完成时由助动词have + 过去分词构成，助动词have 有人称和数的变化。第三人称单数用has，其余用have.
现在完成时的否定式直接在助动词后面加上not、疑问式是把助动词提到主语之前。以study 为例，其否定式、疑问式和简单回答形式如下：
否定式
疑问式
I have not (haven’t) studied….
begin和start区别
Have I studied…?
You have not (haven’t) studied….
Have you studied…?
He has not (hasn’t) studied….
Has he studied…?
否定疑问式
简单回答（肯定/否定）
Have I not (Haven’t I) studied…?
Yes, you have. No, you haven’t.
Have you not (Haven’t you) studied…?
Yes, I have. No, I haven’t.
Has he not (Hasn’t he) studied…?
Yes, he has. No, he hasn’t.
（2）用法：
1）现在完成时通常表示在说话之前已经完成的动作或存在的状态。说话人强调的是该动作或状态对现在的结果或影响。
    My daughter has just gone out. 我女儿刚出去。  I’m sure we’ve met before. 我肯定我们以前见过面。
    She has arrived. 她到了。
2）表示持续到现在的动作或状态，往往和包括现在在内的表示一段时间的状语连用，如recently, already, just, lately, for…, since…,yet等。如：
I haven’t heard from her these days.  这些日子我没有收到她的信。
We haven’t seen you recently.  最近我们没有见到你。
    They have been away for two years.  他们离开已经两年了。  She has been with us since Monday.
★注意：
1）since和for的区别
since后接时间点，如1993，last term, yesterday, the time I got there
for后接一段时间，表示“长达多久”，如ten years, a while, two days等。
Exercise: 用since和for填空
1. Jim has been in Ireland ______ Monday.        2. Jill has been in Ireland ______ three days.
3. His aunt has lived in Australia ______15 days.  4. Mary is in her office. She has been there ______ 7 o'clock.
5. India has been an independent country ______1974.6. The bus is late. They've been waiting ______ 20 minutes.
7. Nobody lives in those houses. They have been empty ______ many years.
8. Mike has been ill ______a long time. He has been in hospital ______ October.
2）表示短暂意义的动词如arrive, leave, borrow, buy, begin, start, die等，在完成时当中不能和表示一段时间的状语连用，因为它们表示的动作不可能持续。因此，不能说：
  He has come here for 2 weeks.  ×
  The old man has died for 4 months.  ×
  They have left only for 5 minutes.  ×
以上三句话可以改为：
He has been here for 2 weeks.
The old man has ______ _______ for 4 months.
They have _____ _____ only for 5 minutes.
3）have (has) been 和have (has) gone的区别：表示“曾到过某地”要用 “have (has) been”;
表示“已经去某地”要用 “have (has) gone”。试比较：
Where has he been?  他刚才到哪里去了？（已经回来了）
Where has he gone?  他上哪儿去了？（人不在）
They have been to Canada. 他们到过加拿大。（现在已经不在加拿大）
They have gone to Canada. 他们到加拿大去了。（可能在路上和已经到加拿大）.
4）现在完成时不能和表示过去的时间状语连用，如yesterday, last year, in 1976, two days ago, just now, when I came in，但可以和already, yet, sometimes, always, often, before, lately, recently, once, twice, ever, never等连用。例如：
She has already come.  她已经来了。
I haven’t read it yet.  我还没读过这个。  I have met him before.  我从前曾见过他。
Ma Hong has always been a good student.  马红一直是个好学生。I have often seen him in the street.  我经常在街上看见他。
They have never been to Yan’an.  他们从未去过延安。  I haven't seen him lately.  我近来没看到他。
Exercise:
I. Fill in the blanks with the proper form.
1. I____ already ____ (see) the film. I ________ (see) it last week. 2. _____ he ____ (finish) his work today? Not yet.
3. My father ____ just ____ (come) back from work. He is tired now.
4. Where’s Li Ming ? He __________ (go) to the teacher’s office.
5. I __________ (work) here since I ______ (move) here in 1999.
6. So far I _______________(make) quite a few friends here.
7. How long ________ the Wangs ______________(stay) here ? For two weeks.
8. I ________ just ___________ (finish) my homework. 9. He ________ (go) to school on foot every day.
10.____ you ______ (find) your science book yet?   11. If it ____ (be) fine tomorrow, I'll go with you.
12. The students ____________ (read) English when the teacher came in.
13. Look! The monkey __________ (climb) the tree.   14. My mother __________ (come) to see me next Sunday.
15. I've lost my pen. _________ you ________ (see) it anywhere?
II. Choose the best answer.
1. How long have you _______ here?
A. come          B. got            C. arrived          D. been
2. My grandpa died _________.
A. at the age of my 2    B. for 2 years    C. when I was 2.    D. my age was 6.
3. Jane has _____ to BeiJing. She will come back tomorrow.
A. been          B. gone          C. went          D. never been
4. It is ten years _____ I last saw her.
A. after          B. since          C. for            D. that
5.--Who will go to the station to meet Lorry?  --I will. I _____ her several times.
A. met          B. have met          C. had met          D. will meet
6. --What a nice dress! How long _____ you _____ it?        --Just 2 weeks.

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