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 20 to 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

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