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
很多人问过这道题了,因为它是强调句,所以用it was ...that.
但为什么不能选when呢?我理解句意是：六百年前第一台钟被制造出来.那六百年前是时间,对于时间应该可以用when的啊.