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