I in the street when I met an old friend of mine yesterday.
A. walked
B. was walking
C. has walked
D. had walked
网友回答
A. walked
(答案→)B. was walking
C. has walked
D. had walked
解析：前半句是主句，沿街散步这个动作是延续性的动作，因而我们用过去进行时。后半句这个时间状语从句的动作，遇到，是个短暂性动作。因为when I met an old friend of mine yesterday.用的是过去式。故排除C。句意：当我看到我的一个老朋友的时候，我正在沿着街道散步。故选B。