完形填空。 It is interesting how NASA (美国航空航天

     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.