I met a friend of mine I was walking along the street.A. beforeB. asC. becauseD. since

问题补充：

I met a friend of mine I was walking along the street.

A. before

B. as

C. because

D. since

答案：

A. before

(答案→)B. as

C. because

D. since

解析：before在……之前； as随着，当……时；because因为；since由于，自从……以来。句意：当我在大街上散步时，我遇到了我的一个朋友。结合语境可知选B。