I was walking to school I saw a boy crying in the street.A. UntilB. WhileC. BeforeD. Afte

问题补充：

I was walking to school, I saw a boy crying in the street.

A. Until

B. While

C. Before

D. After

答案：

A. Until

(答案→)B. While

C. Before

D. After

解析：本题考查连词。句意：当我步行去学校时，我看到一个男孩在街上哭泣。while当……的时候,和……同时。