50. Once the aim _______, he will never give up before he finally achieves it.

　 A. will fix　　　　 B. is fixed　　　　　 C. will be fixed　　　 D. is fixing

49. Mrs. Green was being operated on in the operating room, _______ her three children were waiting

anxiously outside.

A. during which　　　 B. where　　　　　　 C. among which　　　 D. out of which

48. -Look! How busy the building workers are!

　 -Yes, I see. The houses _______ by them will be completed next week.

　　　 A. built　　　 B. being built　　 C. to be built　 D. having been built

47. My daughter always works hard at her lessons and seldom, if ever, _______ late to school.

　 A. she comes　　　　 B. comes she　　　　 C. she does come　　　 D. does she come

46. With a lot of difficult problems_______, the manager felt worried all the time.

A. to settle　　　　 B. settling　　　　 C. settled　　　　 D. being settled