26. We agree to accept _________ they thought was the best tourist guide.
A. whatever
B. whomever
C. whichever
D. whoever
27. Although many people view conflict as bad, conflict is sometimes useful _________ it forces people to test the relative merits of their attitudes and behaviors.
A. by which
B. so that
C. in that
D. provided that
28.A beam of light will not bend round corners unless _________ to do so with the help of a reflecting device.
A. made
B. being made
C. having made
D. to be made
29.A knock at the door again! It was the third time someone _________ me that evening.
A.has interrupted
B. had interrupted
C.to have interrupted
D. would have interrupted
30. The government agrees to install services _________ by residents over a ten-year period.
A. which are to be paid for
B. for which to be paid
C. which to be paid for
D. to be paid for which
试题及答案解析：
26. Dwhoever引导名词性从句，并在从句中做主语，用来指人。they thought 是插入成分。
27. Cin that“是因为”，引导原因状语从句，符合句意。by which表示手段;so that引导目的状语从句;provided that引导条件状语从句。
28.Amade to do so是it is made to do so 的省略形式。unless是连词，应连接句子，所以除A以外的其他几个选项都是错误的。
29.B此处用过去完成时，是因为本句意指“到那次敲门，已经是第三次有人打搅我了”。句中用词was和that evening都说明指过去发生的事，到过去某一时刻为止已出现的情况用过去完成时。
30.Awhich在句中是关系代词，要引导一个句子，而B、C、D三个选项中都没有谓语，因此不是句子。本句意为：“政府同意提供服务设施，经费由居民在十年期间偿还。”
