19．He was busy writing a story, only ______ once in a while to smoke a cigarette.

　　　 A．to stop　　　　　　　　 B．stopping　　　　　　　 C．to have stopped　　 D．having stopped

18．No matter how frequently ______, the works of Shakespeare always attract large audiences.

　 　 A．performed　 　　　 B．performing 　　　　 C．being performed　 D．to be performed

17．I don’t remember how many years ago ______ people began to grow crops.

　 　 A．it was when　 　　 B．it was that　　 　　 C．was it when　　 　　 D．was it that

16．You have no idea how she finished the relay race with her foot　 so much.

　 　 A．to wound　 　　　　 B．wound　　　 　　 C．wounded　 　　　　 D．wounding

15．–-Where did you put the car keys?

--Oh, I _______ I put them on the chair because the phone rang as I _______in.

　　　 A．remembered; come　　　　　　　　　　　　　　　 B．remembered; was coming

　　　 C．remember; come　 　　　　　　　　　　　　　　　　 D．remember; was coming

14．The river beyond our school has become clean again as new measures are ______ to prevent it ______ any further.

　 　 A．taken; polluting　　　　　　　　 　　 B．taking; being polluted

　 　 C．taken; being polluted　 　　　　　　　　 D．taking; to be polluted

13．----What’s happened to George?

　 　----I don’t know．He ________.

　 　　 A．must have got lost　　　　　　　　　　　　　　　 B．may have got lost

　 　　 C．should have got lost　　　　　　　　　　　　　　 D．can’t be lost

12．-Well, I forgot to bring my dictionary here yesterday.

　　　 -Oh, actually you___it here, for dictionaries were not allowed to use here yesterday.

　　　 A．needn’t bring　 　　　　　　　　　　　　　　　　　 B．needn’t have brought　 　　

　　　 C．didn’t need to bring　 　　　　　　　　　　　　　 D．don’t have to bring

11．Yesterday my teacher said to my father with much regret, “Should your son make what his teachers teach _____, he would do much better in his studies.”

　　　 A．him　　　　 　　 B．his　　　 　　　　　 C．himself　　 　　　 D．them　

10．It’s strange that they _____ nothing about this matter.

　　 　 A．should know　　　　 B．would know　　　　 C．had known　　　　　 D．knew