(11)We couldn’t catch up with the others because they _____too long before us.  
 A.started      B.were starting   C.have started    D.had started  

 (12)She felt anxious about her son as she ________for quite a long time.  
  A.haven't heard him           B. hadn’t heard him  
  C.haven‘t heard from him        D. hadn’t heard from him  
 
(13)By the time the speaker entered the hall, all the listeners_______.  
  A. had seated    B. were seated   C. seated       D. were seating  
 
 (14)By the end of next July this building__________.  
  A. will be finished           B. will have finished  
  C. will have been finished       D. had been finished  
 
 (15)By the time the war ____, most of the people had left.  
  A.was began               B. was broken out  
  C.broke out               D. had been broken out  
 
(16)If she ______harder, she would have succeeded.  
  A. had worked    B. have worked   C. should work    D. worked  
 
(17)I wish ______I you yesterday.  
  A. seen       B. did see     C. had seen      D. were to see  
 
(18)He is talking so much about America as if he _______ there.  
  A. had been     B.has been     C. was        D. been
 
(19)That dinner was the most expensive meal we___.  
  A. would have    B. have had     C. had never had   D. had ever had  
 
(20)When Jack arrived he learned Mary ______for almost an hour.  
  A. had gone     B. had set of    C. had left      D. had been away 
 
 【答案解析】
  (11)—(15)D D B C C    (16)—(20)A C A D D