Space is a dangerous place, not only because of meteors (流星) but also becaus

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问题 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 【C1】_____ our protective blanket on earth. Light gets through, and this is 【C2】_____ for plants to make the food 【C3】_____ we eat. Heat, too, makes our environment endurable. Various kinds of rays 【C4】_____ the air from outer space, 【C5】_____ enormous quantities of radiation from the sun are 【C6】_____ off. As soon as men leave the atmosphere they are 【C7】_____to this radiation but their spacesuits or the walls of their spacecraft, 【C8】_____ they are inside, do prevent a lot of radiation damage.
Radiation is the greatest known 【C9】_____ to explorers in space. The unit of radiation is called "rem (雷姆)". Scientists have reason to think that a man can 【C10】_____ far more radiation 【C11】_____ 0.1 rem without being damaged; the figure of 60 rems has been agreed on. The trouble is that it is extremely 【C12】_____ to be sure about radiation damage—a person may feel perfectly well, but the 【C13】_____ of his or her sex organs may be damaged, and this will not be discovered 【C14】_____ the birth of deformed children or even grandchildren.
Missions of the Apollo flights have had to cross belts of high amount of rems. So far, no dangerous amounts of radiation have been 【C15】_____, but the Apollo missions have been quite 【C16】_____. We simply do not know yet how men are going to get on when they 【C17】_____ weeks and months outside the 【C18】_____ of the atmosphere, working in a space laboratory. Drugs might help to 【C19】_____ the damage done by radiation, but no really 【C20】_____ ones have been found so far. [br] 【C19】

选项 A、increase
B、decrease
C、relieve
D、relax

答案 B

解析考查动词词义辨析。由常识可知，药物可帮助减少损伤，故可首先排除A项increase；relieve“缓解，减少”，一般指减轻疼痛等症状，与句意不符；relax“使轻松，放松”强调劳累后休息，也不符合句意；B项decrease意为“减少”，符合句意，故选B。

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