问题
选择题
It was about 600 years ago ______the first clock with a face and an hour hand was made. [ ]
A. that
B. until
C. before
D. when
答案
答案：A
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It was about 600 years ago ______the first clock with a face and an hour hand was made. [ ]
A. that
B. until
C. before
D. when
答案：A
B（g）+C（g），在其它条件不变情况下，