2. 外语
  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【B1】______

Space is a dangerous place, not only because of meteors(流星)but also because of rays from the sun and other stars. The【B1】______

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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【B1】______ again acts as 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】______ off. As soon as men leave the atmosphere they are exposed to this【B5】______ and their spacesuits or the walls of their spacecraft, if they are inside, do【B6】______ a lot of radiation damage.
    Radiation is the greatest known danger to【B7】______ in space. The unit of radiation is called "rem". Scientists have reason to think that a man can put up with 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—【B9】______, 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.【B10】______,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 laboratory. Drugs might help to decrease the damage done by radiation,【B11】______
【B2】
选项
答案essential
解析 此空在系动词“is”后面，可推测这里应填形容词或过去分词作表语。根据前后文大意，不难听出这里是essential，注意要双写s。
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