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 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 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(宇宙的)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 "rem(雷姆)". 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 milligrams; 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.
【C16】
选项 A、conventional
B、common
C、general
D、normal
答案D
解析 conventional“传统的”；common“共同的、普通的”；general“一般的、总体的”； normal“正常的”。本句意为：我们每年接受的正常辐射量……，故选normal‘
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