1.The millions of calculations involved, had they been done by hand, ______all practical value by the time they were finished. A. could lose B. would have lost C. might lose D. ought to have lost
解析：这个句子中含有一个省略if，把助动词提前到主语they之前的虚拟条件句，该条件句表示对过去情况的假设，而主句中by the time they were finished 表明主句也应该是对过去发生的情况的假设，因而应该选(B)would have lost为正确答案。
2. Had Paul received six more votes in the last election, he our chairman now.
A. must have been B. would have been C. were D. would be
解析：这道题目是一个混合虚拟语气的句子。条件句省略了if，把助词had提前到主语前面，表示对过去情况的假设，而主句中now表明了对现在情况的假设，所以应选would(should, could, might)+动词原形这种表达形式。四个选项中只有(D)是正确表达形式，故为正确答案。
3. If you Jerry Brown until recently, you’d think the photograph on the right was strange.
A. shouldn’t contact B. didn’t contact C. weren’t to contact D. hadn’t contacted
解析：until recently，因此(D)是正确答案，而主句是隐含的对现在情况的假设，该句是一个混合虚拟条件句。
4. the English examination I would have gone to the concert last Sunday
A. In spite of B. But for C. Because of D. As for
解析：假设的情况有时不是用一个条件句表示，而是隐含在一个由介词如but for、but that、without, 由连词but、副词otherwise 、比较级、形容词、独立主格等表示的上下文中。本句主句表示对过去情况的假设，但事实上由于英语考试而没有去成，即若不是因为英语考试，我本可以去听音乐会，所以应选(B)But for为正确答案。
5. Look at the terrible situation I am in! If only I your advice
A. follow B. would follow C. had followed D. have followed
解析：题目中的第一句话表示的是现在真实的情况，而第二句话中所要表达的是应该做但事实上没有做的事，这种情况导致第一句话中真实情况的发生，故If only条件句假设的是过去一种情况，因此应该用had +过去分词，所以正确答案是(C)。
6. There is a real possibility that these animals could be frightened, _______a sudden loud noise.
A. being there B. should there be C. there was D. there having been
解析：句意为：“要是有一声巨响，这些动物会受到惊吓，这是有现实可能性的。”should there be表示虚拟条件句中将来时间的谓语形式, if省略,所以should与there倒装。因此B. should there be 就是本题答案 。
7、When Edison died, it was proposed that the American people all power in their homes, streets, and factories for several minutes in honour of this great man.
A. turn off B. turned off C. would turn off D. had turned off
解析： propose是欲望动词,后接的宾语从句或主语从句中谓语要用虚拟语气：should+动词原形或直接用动词原形。选择(A). turn off
8、I apologize if I you, but I assure you it was unintentional.
A. offend B. had offended C. should have offended D. might have offended
解析：B. had offended 。本题测试交错时间的虚拟条件句。was 暗示，事情发生在过去，所以虚拟条件句中的谓语动词应该用表示过去时间的虚拟形式。
9、The board deemed it urgent that these files right away.
A. had to be printed B. should have been printed C. must be printed D. should be printed
解析： D. should be printed 。因为urgent是欲望形容词,在句中作形式宾语it的补足语,所以宾语从句中的谓语需用虚拟语气:(should)+动词原形(主动态或被动态)。
10、 The board deemed it urgent that these files right away.
A. had to be printed B. should have been printed C. must be printed D. should be printed
解析：it是形式宾语，urgent是宾语补足语，that引导的从句是真正的宾语从句，该从句的内容被认为是urgent(急迫的)，这样从句的谓语动词要求用虚拟语气形式，即should(可以省略)+动词原形。因此，本题正确答案是(D)。
11、 Jean Wagner’s most enduring contribution to the study of Afro-American poetry is his insistence that it in a religious, as well as worldly, frame of reference.
A. is to be analyzed B. has been analyzed C. be analyzed D. should have been analyzed
解析：(C)在表示要求、愿望、建议、请求、命令等含义的名词同位语从句中，从句谓语动词要用虚拟语气形式，即should(可以省略)+动词原形。
12、I would have gone to visit him in the hospital had it been at all possible, but I ____ fully occupied the whole of last week. A. were B. had been C. have been D. was
解析：(D)本道题目的前半句话是对过去情况的一种假设，但事实上并没有发生，而事实上没有发生的真实原因是句子的后半部分由but引导的转折句所表述的真实。因而but所引导的句子中应该用表示志过去事实相符合的表陈述的时态，即一般过去时。
13. I apologize if I you, but I assure you it was unintentional.
A. offend B. had offended C. should have offended D. might have offended
解析：(B)此题要求在if从句中选择适当的动词形式，以主句中的动词apologize(抱歉)来看，if从句中表达的内容应该是过去做的事，因此可以排除(A)，因为(A)是现在时。(C)中should+have+过去分词结构表示本来应该做却没有做的事，在此不合题意。(D)选项中的might+have+过去分词表示对过去发生的事情很不肯定的猜测，它表达的内容还不能成为事实，所以藉此道歉真是不知从何说起，因此此处也不合题意。(B)had offended表示当时已经发生了的动作。这是复杂条件句：apologize 是现在，而条件句是表示对过去假设的条件句。
14. If you hadn’t taken such a long time to get dressed, we’d there by now.
A. be B. circles C. is circling D. be circling
解析：该句也是一个复杂条件句(或称作混合虚拟条件句)。条件句表示对过去情况的假设，而主句表示对现在情况的假设，但事实上却与此相反，所以正确答案应该是(A)。
15. The sun rises in the east and sets in the west, so it seems as if the sun ________round the earth.
A. were circling B. circles C. is circling D. be circling
解析：if引导的从句要求用虚拟语气，表示同时或将来的情况，动词要用过去式(be动词用were)或would(could等)+动词原形，本句话中指的是当时的情况，所以要用过去式，故(A)是正确答案。
16. If the Watergate Incident Nixon would not have resigned from the presidency.
A. did not occur B. had not occurred C. was not occurring D. be circling
解析：(B)had not occurred表示对过去的虚拟，条件句中要用过去完成式，主句中要用should(would, could, might)+动词原形的过去分词。
17. I hadn’t expected James to apologize but I had hoped .
A. him calling me B. that he would call me C. him to call me D. that he call me
解析：(B)had hoped是常见的要求其后的宾语从句用虚拟语气的句型,虚拟语气would+动词原形。
18. George would certainly have attended the proceedings .
A. if he didn’t get a flat tire B. if the flat tire hadn’t happened
C. had he not had a flat tire D. had the tire not flattened itself
解析：表示对过去情况的假设，主句动词形式为would(should, could, might)+have+过去分词，条件句为过去完成式，if可以省略，但要把had提前主语前面。(B)，(D)的表达不符合英语表达习惯，所以(C)是正确答案。
19. The teacher suggested that her students experiences with ESP.
A. write a composition on their B. to write composition about the
C. wrote some compositions of his or her D. had written any compositions for his
解析：(A)suggest后面的从句要用虚拟语气形式，其形式为should(可以省略)+动词原形。
20. He speaks Chinese as fluently as if he ______a Chinese.
A. were B. had been C. is D. has been
解析：(A).表示与现在相反的虚拟。
