Mingming lost his key while he___across the road
问题描述：
Mingming lost his key while he___across the road
A.ran B.has run c.was running D.had run
答
C 表示在一个动作发生的同时发生来另外一件事情
其实也可以用when 来改写的：Mingming was running across the road when he lost his key.