Question

--- Did you see the traffic accident yesterday?

--- Yes. It happened when I ________ past the museum.

[　　]

A．walk

B．am walking

C．will walk

D．was walking

Answer 1

答案：D
解析：

when引导时间状语从句，意为“当……时候”，主从句时态要一致，主句为一般过去时，故从句只能为过去的某种状态。