完形填空。 It is interesting how NASA (美国航空航天管理局) chose their astronauts (宇航员) for landing them on the moon. They chose men__1______the age of twenty and thirty-five. There were about fifty of them. Many were __2___ air pilots.__3__were scientists with two or three degrees. NASA telephoned each man they were going to choose, told them the plans and the __4__ they might get in. They then asked him if he was willingto be trained as an astronaut. 'How could any man __5__ such an exciting job?' one of them said. 'Dangerous? Of course, it's dangerous, __6__ most exciting! ' The health and physical condition of __7__ was, of course, very necessary. __8__ those in very good health and physical condition were chosen. While being trained to be astronauts, they went through many__9__. They studied the stars and the moon, and they also studied geology, the science of rocks. This was necessary__10__astronauts would have to look for rocks on the moon. They would try to find rocks which might help to tell the __11__ of the moon. They were all__12__to fly in helicopters. These helicopters landed __13__ down to give them some experience of the way the spaceship would.__14__land on the moon. They were also taught all the __15__ facts about the conditions. They learnt all the technical details of the spaceships and rockets. They visited the scientists and engineers who __16__ them. They visited the factories where they were __17__ .They learnt how every__18__of a spaceship and its instruments work. They also learnt every detail of ground-control __19___ . In a word, to be chosen as an astronaut, one must be in good health,__20__in science and good at piloting. (     )1.A. at (     )2.A. experienced (     )3.A. None (     )4.A. danger (     )5.A. accept (     )6.A. but (     )7.A. the scientists (     )8.A. As (     )9.A. jobs (     )10.A. for (     )11.A. story (     )12.A. shown (     )13.A. straight (     )14.A. possibly (     )15.A. not known (     )16.A. drew (     )17.A. repaired (     )18.A. part (     )19.A. house (     )20.A. well-done B. between B. old B. Few B. sadness B. receive B. if B. men B. Only B. places B. because B. background B. trained B. straightly B. likely B. well-known B. produced B. built B. movement B. stop B. well fed C. of C. trained C. Others C. hardship C. offer C.though C. pilots C. If C. courses C. since C. age C. told C. indirectly C. actually C. unknown C. designed C. developed C. machine C. system C. well-kept D. on D. young D. They D. troubles D. refuse D.however D. young people D. Or D. ways D. so that D. name D. let D. directly D. really D. known D. made D. fixed D. body D. station D. well-informed