单项选择题

The best title for this passage would be

A．The Atmosphere and Our Environment
B．Research on Radiation
C．Effects of Space Radiation
D．Importance of Protection Against Radiation
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单项选择题
The harm radiation has done to the Apollo crew members______.
A．is insignificant
B．seems overestimated
C．is enormous
D．remains unknown
单项选择题
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
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