21.—I wonder how much you charge for your services.

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

　　A.while B.until

　　C.when D.before

　　答案：A　考查連詞的用法。while表對比，意為“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　考查狀語從句。where引導的地點狀語從句。句意為：她總是把貴重的東西，比如首飾、錢等放在她認為安全的地方。

　　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　考查條件狀語從句。分析題干的邏輯關系可知，后句是前句的條件，所以用only if。句意：只要他自己付錢吃飯，我就接受Guy和我們一起去。

　　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　考查特殊句式和狀語從句。句意為：不管這本書多么有趣，那個孩子看起來是絕不會把它看完的。感嘆句的詞語排列順序為：how+形容詞+冠詞+可數(shù)名詞單數(shù)=what+冠詞+形容詞+可數(shù)名詞單數(shù)。根據(jù)句意可知，此處表示“不論到什么程度，不管”，故應用however，故答案A符合語境。

　　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 if