问题
选择题
________ there are living creatures in the outer space as those on Earth hasn't been proved until now.
A．How
B．When
C．Where
D．Whether
答案
答案：D
D 考察主语。句意：在外部空间是否有与地球相同的生物直到现在还没有得到证明。Whether引导主语从句，意为是否。
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