【单选题】

Space is a dangerous place, not only because of meteors (流星) but also because of rays from the sun and other stars. The atmosphere again acts (67) our protective blanket on earth. Light gets through, and this is (68) for plants to make the food (69) we eat. Heat, too, makes our environment endurable. Various kinds of rays (70) through the air from outer space, (71) enormous quantities of radiation from the sun are (72) off.As soon as men leave the atmosphere they are (73) to this radiation but their spacesuits or the walls of their spacecraft, (74) they are inside, do prevent a lot of radiation damage.

Radiation is the greatest known (75) to explorers in space. The unit of radiation is called "rein (雷姆)". Scientists (76) reason to think that a man can put up with far more radiation (77) 0.1 rem without being damaged; the figure of 60 rems has been agreed on. The trouble is that it is extremely (78) to be sure about radiation damage-a person may feel perfectly well, but the (79) of his or her sex organs may be damaged, and this will not be discovered (80) the birth, of deformed children or even grandchildren.
Missions of theApollo flights have had to cross belts of high amount of reins. So far, no dangerous amounts of radiation have been (81) , but theApollo missions have been quite (82) . We simply do not know yet how men are going to get on when they (83) weeks and months outside the (84) of the atmosphere, working in a space laboratory.Drugs might help to (85) the damage done by radiation, but no really (86) ones have been found so far.
A、increase B、decrease
C、relieve D、relax