Mary and I have been close friends we met each other 10 years ago.A. whenB. sinceC. until

问题补充：

Mary and I have been close friends we met each other 10 years ago.

A. when

B. since

C. until

D. as

答案：

A. when

(答案→)B. since

C. until

D. as

解析：考查连词：A. when当…时候B. since自从C. until直到. As因为，句意：玛丽和我自从前认识，一直是好朋友。选B。