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  3. 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

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

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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【B1】______our protective blanket on earth. Light gets through, and this is【B2】______for plants to make the food which we eat. Heat, too, makes our environment【B3】______. Various kinds of rays come through the air from outer space, but enormous quantities of radiation from the sun are【B4】______. As soon as men leave the atmosphere they【B5】______this radiation and their spacesuits or the walls of their spacecraft, if they are inside, do prevent a lot of radiation damage.
    Radiation is the greatest known danger to【B6】______in space. The unit of radiation is called "rem". Scientists have reason to think that a man can【B7】______far more radiation than 0.1 rem without being damaged: the figure of 60 rems has been agreed on. The trouble is that it is【B8】______difficult to be sure about radiation damage—a person may feel perfectly well, but the cells of his or her sex organs may be damaged, and this will not be discovered until the birth of deformed children or even grandchildren. Missions of the Apollo flights have had to cross belts of high amounts of rems. So far, no dangerous amounts of radiation have been reported, but the Apollo missions have been quite short, we simply do not know yet how men are going to get on, when they spend weeks and months outside the protection of the atmosphere, working in a space【B9】______. Drugs might help to decrease the damage done by radiation, but no really【B10】______ones have been found so far.
【B5】
选项
答案are exposed to
解析 空格所在句缺谓语，故此空需填动词。beexposed to“暴露于……”，由于本段均为一般现在时，而该句主语为they，故be动词用are。
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