单项选择题

It can be inferred from the passage that ______.

A．the Apollo mission was very successful
B．protection from space radiation is not a easy job
C．astronauts will have deformed children or grandchildren
D．radiation is not a threat to well-protected space explorers

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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 spacesuit 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