Space is a dangerous place,not only because of meteors but also because of rays from the sun?and other stars.The atmosphere again acts as our protective blanket on earth.Light gets through,and?this is essential for plants to make the food which we eat.Heat,too,makes our environment endurable.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 exposed 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 danger to explorers in space.The unit of radiation is called"rein".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 extremely?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(畸形的)children or even grandchildren.Missions of the Apollo flights have had to cross belts of high radiation?and,during the outward and return journeys,the Apollo crew accumulated a large amount 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 laboratory.Drugs might help to decrease?the damage done by radiation,but no really effective ones have been found so far.
The best title for this passage would be__
【考情点拨】主旨大意题。【应试指导】通读全文可知，文章开头提到，宇宙空间里存在很多辐射，第二段又紧紧围绕辐射对人类的影响展开论述。C项符合题意，故选C。
我国独立自主的外交政策体现在哪些方面？我国为什么必须实行对外开放？
简述人民民主专政理论的基本内容。
简述走农村包围城市，武装夺取政权道路的必要性。
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遵义会议集中解决了党的政治路线问题。
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对外开放是我国的一项长期的基本国策，实行这一国策的前提和基础是（ ）
计划和市场是（ ）
加强党的自身建设，必须放在首位的是（ ）
中国共产党的立党之本、执政之基、力量之源是（ ）
