While ___ along the street, I met an old friend of mine.
A. I walking B. was walking C. I am walking D. walking
While ___ along the street, I met an old friend of mine.
A. I walking B. was walking C. I am walking D. walking
D
本题考查了省略。在时间状语从句、条件状语从句和让步状语从句中，如果主句的主语与从句的主语一致，谓语含有动词be，经常采用省略的形式，如He never speaks to anyone unless (he is ) spoken to. A, B句子结构错误；C时态错误。