1. clothes, cloth, clothing
clothes统指各种衣服，谓语动词永远是复数， cloth指布，为不可数名词 clothing 服装的总称，指一件衣服用a piece of, an article of

2. incident, accident
incident指小事件, accident指不幸的事故He was killed in the accident.

3. amount, number
amount后接不可数名词， number后接可数名词 a number of students

4. family, house, home
home 家，包括住处和家人，house房子，住宅，family家庭成员. My family is a happy one.

5. sound, voice, noise
sound自然界各种各样的声音，voice人的嗓音，noise噪音I hate the loud noise outside.

A. 现在完成时: 1)表示过去某时发生的行为对主语目前产生的影响。即用过去发生的某个行为来说明现在的某种情况。往往含有“已经……”, “已经……了”的意思。
Eg.Don’t think any more about it. I have decided not to help you.
I have experienced that before, so I know how to deal with it.

2) 到目前为止已发生的。与so far, up till now, in the past/ last …….days/ years, today, this month/ year 等 “包括现在在内的时间状语”连用。
My brother is an actor. He has appeared in several films so far.
Great changes have taken place in this area in the recent years.

3）表示过去开始的动作或状态延续到现在。与for…/ since 连用。
He has worked in the south for ten years/ since ten years ago.

Compare

(1):完成进行时表示过去开始的动作一直在进行，直至现在。
He has been working on this project since last month.

(2) 过去时态:指发生在过去某段时间内的事。
He once worked in the south for ten years (现在不在南方)

(3) 过去完成时态:指发生在过去某个时间以前的动作或状态。常与by/ by the end of..(到了……的时候”连用。例如：
1）By the time we got to the theatre, they had sold all the tickets.
2）How many words had you leaned by the end of last year?

Practice:
1.It is reported that the president once______ in the Viet Nam’s war for three years from 1966-1970.   
A. served   B. had served  C. has served  D. was serving

2. ---No one answered when I called at 6 yesterday.
  ---I ________ to rock music and was absorbed in it.
A listened  B was listening  C. has listened  D. had listened

3.I wasn’t paying attention to what he was talking about, so I am afraid I ___ his speech very well.
A. had not understood  B. has not understood   C. did not understand  D. don’t understand

4. I _____ good at table tennis, but I haven’t played it for ages.
A. am   B. was   C. has been  D. used to be

5. I _________ where she gets her money all these days.
A. am often wondering  B. often wondered  C. had often wondered D．have often wondered

6. ---Tell me what _______ while I was absent.
  ---A thief tried to break into the house when I _______ in your house.
A. happened/ stayed         B. was happening/ was staying
C. happened/ was staying      D. was happening/ stayed

7. ---You are always watching TV.
  ---Only on Sundays. And nobody ______ it but you.
A. knows   B. has known  C. knew  D. is knowing

8. When the old man ______ to walk back to his house ,the sun _____ itself behind the mountain.
A．started ;had already hidden    B．had started ;had already hidden
C．had started ;was hiding        D．was starting; hid

9. Years ago we didn't know this, but recent science ______ that people who don't sleep well soon get ill.      
A. showed    B. has shown     C. will show    D. is showing

10. It ______ for weeks before the first cold wave struck the area.
A. rained   B. was raining  C. has rained   D. had been raining


Keys:1)a 2)b. 3)c 4)a 5) 过去到现在d 6) c 7)a(经常性) 8)a 9) b 与现在有联系 10)d