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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.
【B8】
选项
答案extremely
解析 该句子不缺主要成分，推测这里应填入一个副词，用以修饰difficult，表程度。extremely表示“很，非常，极端地”，拼写时注意不要漏写里面的e。
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