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
网友回答
(答案→)A. that
B. until
C. before
D. when
解析：考察句型。该句为强调句，强调句的特点是去掉It was ……that……以后句子结构完成。即，the first clock with a face and an hour hand was made about 600 years ago 句子结构完整。