Grammar

15. He [D. had played] football regularly for many years when he was young.
A. was playing B. played C. has played D. had played

16. John promised his doctor he [D. would] not smoke, and he has never smoked ever since.
A. might B. should C. could D. would

17. There’s no light on — they [A. can’t] be at home.
A. can’t B. mustn’t C. needn’t D. shouldn’t

18. The growing speed of a plant is influenced by a number of factors, [A. most of them] are beyond our control.
A. most of them B. most of what C. most of which D. most of that

19. [D. As] is known to all, good friends [add to] happiness and value to life.
A. It; add to B. It; add C. As; add D. As; add to

20. [B. Walking] in the fields on a March afternoon, he could feel the warmth of spring.
A. To walk B. Walking C. Walked D. Having walked

21. Either you or one of your students [B. is] to attend the meeting that is due tomorrow.
A. are B. is C. have D. be

22. It is reported that the United States uses [D. twice as much] energy as the whole of Europe.
A. as twice B. twice much C. twice much as D. twice as much

2014-10-20 02:48:14 補充：
Because I was wrong. (It was done in a hurry! Sorry!)

Q18:
As It is a relative clause, the answer should be: C. most of which

2014-10-20 02:58:04 補充：
Q19: 意I思A 知識長 is correct.Thanks. 這是我的疏忽大意。

"happiness and value" is a compound noun, as the object of the verb "add".

2014-10-20 03:06:29 補充：
第19題: 意I思A 知識長 is correct.Thanks. 這是我的疏忽大意。

"happiness and value" is a compound noun, as the object of the verb "add".

2014-10-20 03:13:34 補充：
第18題: 意I思A 知識長 is correct.Thanks.

As it is a relative clause, the answer should be: C. most of which

"which" is the relative pronoun that stands for "factors".

I agree with 意I思A ( 知識長 )

15. [B. played]

The past perfect expresses a past action completed prior to another event or time in the in the past.
When he was young, he played football regularly.
不要因 ”for many years“ 誤導, 要看 ”when he was young.”. 兩個 clauses refer 同一時期, 不是 sequence of events.

2014-10-20 07:56:28 補充：
15. He [B. played] football regularly for many years when he was young.

Compare:
Use of past perfect

He had played football regularly for many years before he turned professional in 1999.
When they got married, they had known each other for ten years.

第15題,19題我同意Dustin的答案,因為15題有for many yrs,用past tense不太恰當
另外19題 value to life,所以前面也要一致add to happiness

但可以解釋一下16題,你為何選c???? 我對於16不太明白

15. He [B. played] football regularly for many years when he was young.
18. The growing speed of a plant is influenced by a number of factors, [C. most of which] are beyond our control.
19.[C . As] is known to all, good friends [add] happiness and value to life.