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
We know from the passage that ______.
A．exposure to even tiny amounts of radiation is fatal
B．the effect of exposure to radiation is slow in coming
C．radiation is avoidable in space exploration
D．astronauts in space suits needn't worry about radiation damage
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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