A. endurable B. protection C. exposed D. if E. untilF. extremely G. acts as H.

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问题 A. endurable B. protection C. exposed D. if E. until
F. extremely G. acts as H. decrease I. curable J. disaster
K. attributed L. danger M. effective N. before O. essential
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【C1】______ our protective blanket on earth. Light gets through, and this is【C2】______ for plants to make the food we eat. Heat, too, makes our environment【C3】______. Various kinds of rays come through the air from outer space, but enormous quantities of radiation from the sun are screened off. As soon as men leave the atmosphere they are【C4】______ to this radiation but their spacesuits or the walls of their spacecraft, if they are inside, do prevent a lot of radiation damage.
Radiation is the greatest known【C5】______ to explorers in space. The unit of radiation is called "rem (雷姆)". Scientists have reason to think that a man can put up with far more radiation than 0.1 rem without being damaged. The trouble is that it is【C6】______ 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【C7】______ the birth of deformed children or even grandchildren.
We simply do not know yet how men are going to get on when they spend weeks and months outside the【C8】______ of the atmosphere, working in a space laboratory. Drugs might help to【C9】______ the damage done by radiation, but no really【C10】______ ones have been found so far. [br] 【C7】

选项

答案 E

解析空格所在句讲什么时候发现辐射的危害。备选项中的介词until与否定词构成not．．．until“直到……才”结构，符合句意，故选E。

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