单项选择题


A．At the same time
B．On the contrary
C．For example
D．In a word
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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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