21. As usual, he put on a show as though his trip a great success.
A. had been B. has been C. were D. was
解析：A.as though引导的与过去相反的虚拟。
22. Looking round the town, he felt as though he away for ages.
A. has been B. was C. is D. had been
解析：D.felt是过去式，所以该句是由as though引导的与过去相反的虚拟。
23. John is so strongly built that he looks as if he as elephant.
A. lifts B. is lifting C. lifted D. could lift
解析：D.as if引导的与现在事实相反的虚拟。
24. He described the town as if he it himself.
A. had seen B. has seen C. saw D. sees
解析：A.as if引导的与过去相反的虚拟。
25. Most insurance agents would rather you anything about collecting claims until they investigate the situation.
A. do B. don’t C. didn’t D. didn’t do
解析：(D)would rather后接从句要求用虚拟语气，形式为过去式，表示对现在或将来的假设，或为过去完成式表示对过去的情况的假设。
26. Although most adopted persons want the right to know who their natural parents are, some who have found them wish that they the experience of meeting.
A. hadn’t B. didn’t have had C. hadn’t had D. hadn’t have
解析：(C)who引导的定语从句中的现在完成时表示动作业已发生，所以主句中表示的虚拟是针对已经发生了的行为，所以应该用过去完成式表示对过去的虚拟。
27. Without electronic computers, much of today’s advanced technology .
A. will not have been achieved B. have not been achieved
C. would not have been achieved D. had not been achieved
解析：(C)这是一人含蓄虚拟条件句，通过介词短语without,表示潜在的一种假设，而主句中的情况也早已经发生，所以是对过去情况的一种假设，因此用would not have been achieved这一形式。
28. He told her to return the book in time so that others a chance to read it .
A. may have B. will have C. would have D. might have
解析：(D)连so that引导的从句中要求用虚拟语气，表示一种假设，形式为might+动词原形。
29. It is time that the government measures to protect the rare birds and animals.
A. takes B. took C. has taken D. taking
解析：(B)It is time that是一种要求从句用虚拟语气的常见句型。虚拟语气形式为动词的过去式。
30. He was very busy yesterday, otherwise he to the meeting.
A. would come B. came C. would have come D. had come
解析：(C)otherwise用来表示一种含蓄的虚拟假设，因为是对过去(yesterday)的情况的假设，所以应该用would have come形式。
31. I must say he reads very well, and I shouldn’t be surprised if he acting for a living one day.
A. had taken up B. takes up C. have taken up D. would have taken up
解析：(B)所给的四个选项中没有一个表示对未来的情况的虚拟的形式should+动词原形，或是were to do，因此可以断定if引导的条件句在这里最真实的条件句，用一般现在时表示一般将来时，故(B)是正确答案。
32. If I had seen the movie, I you all about it now.
A. would tell B. will tell C. have told D. would have told
解析：(A)这是一个混合虚拟语气的句子，if条件句表示的是对过去情况的假设，而主句是对现在(now)的情况的假设，故用would tell形式。
33. I’d rather you anything about it for the time being.
A. do B. didn’t do C. don’t D. didn’t
解析：B.would rather引导的虚拟语气其谓语用过去式。
34. Mary my letter; otherwise she would have replied before now.
A. has received B. ought to have received C. couldn’t have received D. shouldn’t have received
解析：C.注意单词otherwise引导虚拟语气。
35. We didn't know his telephone number, otherwise we _____ him. ( 1995年6月四级第46题)
A) would have telephoned B) must have telephoned C) would telephone D) had telephoned
解析：本题是与过去时相反的虚拟句，从句中用过去完成式，主句中用would have done。本句相当于if we had known his telephone number，we would have telephoned him。答案是(A) would have telephoned。
