—The first two are free ________ the third costs $30.

A.while B.until

C.when D.before

答案：A　考查连词的用法。while表对比，意为“而”。

22. How can they expect to learn anything ________ they never listen?

A.whether B.when

C.but D.unless

23. She usually keeps her valuables, such as jewels and money, ________ she believes secure.

A.even if B.in case

C.where D.that

答案：C　考查状语从句。where引导的地点状语从句。句意为：她总是把贵重的东西，比如首饰、钱等放在她认为安全的地方。

24.Please call my secretary to arrange a meeting this afternoon, or ________ it is convenient to you.

A.whenever B.however

C.whichever D.wherever

25.——Did you inform Helen of the plan put forward at the meeting?

—Of course. ________ I saw her.

A.So long as B.If only

C.The moment D.Any time

26. Scientists are warning that ________ emissions of carbon (碳排放) are cut, we could be heading for an environmental disaster.

A.before B.as

C. unless D.in case

27. I will accept Guy coming with us, ________ he pays for his own meals.

A.only if B.so that

C.ever since D.even though

答案：A　考查条件状语从句。分析题干的逻辑关系可知，后句是前句的条件，所以用only if。句意：只要他自己付钱吃饭，我就接受Guy和我们一起去。

28. ________ H7N9 is a deadly virus, it is still safe to eat thoroughly­cooked chicken.

A.Until B.While

C.If D.Since

29. The movie Life of Pi is so attractive that it holds the audience's curiosity ________ the story reaches the end.

A.until B.before

C.after D.when

30. Jerry has promised to keep the secret, so he won't tell anyone ________ asked to.

A.until B.now that

C.unless D.even though

31. It will be another 50 years ______ our country is expected to reach the level of a medium developed country.

A.since B.before

C.that D.when

32. House prices vary from place to place and are usually high ________ there are famous schools.

A.when B.since

C.where D.whether

33. We can't wait any longer ________ we'll miss the plane.

A.or B.but

C.so D.yet

34. The new system needs to be in operation for five months ________ it can be updated.

A.as B.while

C.before D.once

35. ________ it is, the boy never seems to be able to finish it off.

A.However interesting a book

B.Whatever interesting a book

C.How interesting a book

D.What an interesting book

答案：A　考查特殊句式和状语从句。句意为：不管这本书多么有趣，那个孩子看起来是绝不会把它看完的。感叹句的词语排列顺序为：how+形容词+冠词+可数名词单数=what+冠词+形容词+可数名词单数。根据句意可知，此处表示“不论到什么程度，不管”，故应用however，故答案A符合语境。

36. Steve was busy clearing the cups and dishes from the table ________ others were playing.

A.until B.if

C.since D.while

37.You seem to have a ready­made answer ________ I ask you a question.

A.whenever B.whatever

C.whichever D.whoever

38.—I don't mind how you do it ______ you finish the painting on time.

—OK, I see.

A.as well as B.as far as

C.as long as D.as fast as

39.—Was it 11 o'clock ________ your father came back last night?

—Yes, he is always coming back so late.

A.that B.while

C.when D.until

40. ________ you need something, please don't hesitate to let me know.

A.Even though B.In case

C.As though D.Even if41.Mr. Smith doesn't go to his usual club, ________ it is being decorated these days.