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【C2】______. Light gets through, and this is essential【C3】______plants to make the food which we【C4】______. Heat,【C5】______, makes our environments tolerable and some ultraviolet rays(紫外线) penetrate the【C6】______. Cosmic rays of various kinds come【C7】______the air from outer space, but【C8】______quantities of radiation from the sun are screened off.【C9】______ men leave the atmosphere they are【C10】______to this radiation;【C11】______their spacesuits or the walls of their spacecraft, if they are inside,【C12】______prevent a lot of radiation damage. Radiation is the greatest known danger to explorers in【C13】______. Doses of radiation are measured in【C14】______called "rems" (雷目). We all【C15】______radiation here on earth from the sun, from cosmic rays, and from radioactive minerals. The"【C16】______"dose of radiation that we receive each year is about two millirems; it【C17】______according to where you live, and this is a very rough estimate. Scientists have reason to think【C18】______a man can【C19】______far more radiation【C20】______without being damaged; the figure of 60 rems has been agreed. [br] 【C17】

选项 A、shifts
B、converts
C、modifies
D、varies

答案 D

解析 shift“移动”；convert“转换”；modify“修改”；vary“变化”。根据句意，所处地点不同，所受辐射量也不一样，故选varies。

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