【单选题】
{{B}}Directions:{{/B}}
Read the following text.Choose the best word(s) for each numbered blank and markA,B,C、orD、onANSWER SHEET 1.
Space is a dangerous place, not only because of meteors (流星) but also{{U}} (1) {{/U}}rays from the sun and other stars. The atmosphere again{{U}} (2) {{/U}}as our protective blanket on earth. Lightgets through, and this is essential for plants to{{U}} (3) {{/U}}the food which we eat. Heat, too, makes our environment endurable. Various kinds of rays come through the air{{U}} (4) {{/U}}outer space, but enormous quantities of radiation from the sun are{{U}} (5) {{/U}}off.As soon as men leave the atmosphere they are{{U}} (6) {{/U}}to this radiation, but their space suits or the walls of their spacecraft, if they are inside,{{U}} (7) {{/U}}prevent a lot of radiation damage.{{U}} (8) {{/U}}is the greatest known danger to explorers in space. The unit of radiation is called "rem". Scientists have{{U}} (9) {{/U}}to think that a man can{{U}} (10) {{/U}}far more radiation than 0.1 ram without being damaged: the figure of 60 rems has been agreed on. The trouble is that it is extremely difficult to make{{U}} (11) {{/U}}about radiation damage—a person may feel perfectly well,{{U}} (12) {{/U}}the cells of his or her sex organs may be damaged, and this will{{U}} (13) {{/U}}be discovered until the birth of deformed children or even grandchildren. Missions of theApollo flights have had to cross belts of high radiation and during the outward and return journeys, theApollo crew{{U}} (14) {{/U}}a large amount of rems. So far; no{{U}} (15) {{/U}}amounts of radiation have been reported, but theApollo missions have been quite short. We simply do not know yet how men are. going to{{U}} (16) {{/U}}when they spend weeks and months outside the{{U}} (17) {{/U}}of the atmosphere,{{U}} (18) {{/U}}in a space laboratory.Drugs might help to{{U}} (19) {{/U}}the damage done by radiation, but no really{{U}} (20) {{/U}}ones have been found so far.
A．guard
B．cover
C．layer
D．protection
网考网参考答案：D
网考网解析：在第一段中已经讲到了大气层的作用是保护性质的，因此此处应该选protection，意思是没有了大气的保护，他们是怎么生活的。
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