Not so long ago it was assumed that the dangers man would meet in space would be 11 , the main ones being radiation and the danger of being hit by meteors. It is perhaps 12 remembering that less than two centuries ago, the dangers of train travel seemed 13 terrible. A man would certainly die, it was thought, if carried along at a speed of 30 m. p. h.
　　There are two sorts of radiation man must fear in space. The first is from the sun, which is 14 The second, less harmful form, comes from the so-called Van Allen Belts. These two kinds of radiation are as far as about 1,500 miles away from the earth. Neither of these forms of 15 is dangerous to us on the earth, since we are protected by our atmosphere. Specifically, it is that part of our atmosphere 16 as the ozonosphere which protects us. This is a belt of the chemical ozone between 12 and 21 miles from the 17 which absorbs all the radiation.
　　Once outside the atmosphere, however, man is no longer protected, and radiation can be harmful in a number of ways. A distinction must be drawn between the short and long-term effects of radiation. The 18 are merely unpleasant, but just because an astronaut 19 from a journey in space does
　　not seem to have been greatly harmed, we cannot assume that he is safe.  The long-term effects can be extremely serious, even 20to death.

　　A.  guiding    B.  terrible     C.    leading    D.    worthy
　　E. known       F.  similarly   G.    deadly     H.    projection
　　I.  returning   J.  formal      K.    radiation  L.    worth
　　M.  ground    N.  meanwhile      O.    former   

　　答案：11. B 12. L 13. F 14. G 15. K 16. E 17. M 18. O 19. I 20. C