Radiation is the greatest known danger to explorers in space. The unit of radiation is called "rem". 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 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.
According to the first paragraph, the atmosphere is essential to man in that ______.
A. it protects him against the harmful rays from space
B. it provides sufficient light for plant growth
C. it supplies the heat necessary for human survival
D. it screens off the falling meteors
利用市场上同样或类似资产的近期交易价格,经过直接比较或类比分析以估测资产价值的各种评估技术方法是()。
A. 成本法
B. 收益法
C. 分析法
D. 市场法