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
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。