单项选择题

Only outside the Earth's atmosphere ______ to attain extremely high velocities.

A．to be safe for a space vessel
B．is safe for a space vessel
C．for a space vessel to be safe
D．a space vessel to be safe
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单项选择题
B
单项选择题
A． On Saturday. B． On Monday. C． On Tuesday.
A． On Saturday.
B． On Monday.
C． On Tuesday.
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