问题
选择题
It was not until the beginning of the twentieth century________to explore space.[ ]
A．did man begin
B．when man began
C．that man began
D．then man began
答案
答案：C
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It was not until the beginning of the twentieth century________to explore space.[ ]
A．did man begin
B．when man began
C．that man began
D．then man began
答案：C