15. — Come on in, Peter. I want to show you something.
—Oh, how n ce of you! I ____ you ____ to bring me a gift.
A. never think, are going
B. never thought, were going
C. didn’t think, were going
D. hadn’t thought, were going
答：D。I never thought ...意为“我从没想到……”，当主句用过去时，从句应用过去进行时。C项属于否定转移，意为：“我认为你不会……。”
16. Tom__________ his bike and has to go to school on foot every day now.
A. lost B. is losing
C. had lost D. has lost
答：D。一般过去时单纯指过去的情况，和现在没有联系。而现在完成时则强调对现在产生的结果或影响．若选A项，他过去把自行车丢了，现在有没有白行车不清楚。
17. —Have you finished the work’?
—No. I ____ you wanted me to do it at once.
A. don’t realize B. didn’t realize
C. haven’t realized D. am not realizing
答：B．“我没有意识到”是指早没有意识到，以前没有意识到，故应用一般过去时。
18. The police found that thc house__________ and a lot of things
A. has broken into. has stolen
B. had broken into, had been stolen
C. has been broken into. stolen
D. had been broken into, stolen
答：D。过去完成时表示动作发生在过去的过去，根据found一词可判断用过去完成时，应用被动语态．stolen是had been stolen的省略式。
19. When I was at college f__________ three foreign languages, but l__________ all except a few words of each.
A. spoke, had forgotten
B. spoke, have forgotten
C. had spoken, had forgotten
D. had spoken, have forgotten
答：B．“我在大学时，能说二门外语”应用过去时，“但现在都已忘了”应用现在完成时，强调对现在产生的结果或影响。
20. The students __________ busily when Miss Brown went to get a book she________ in the office.
A. had written, left
B. were writing, has left
C. had written, had left
D. were writing, had left
答：D．when意为“当……时”，表示当一个动作发生时，另一动作正在进行。根据句中的时态可知，后一空用had left，表示动作发生在过去的过去。