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。

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。

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。

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。

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。

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。

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)。

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。

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。

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。