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

It was about 600 years ago _______ the first clock with a face and an hour hand was made.

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

It was about 600 years ago ______ the first clock with a face and an hour hand was made．

1. A.
   that
2. B.
   until
3. C.
   before
4. D.
   when