he___ his homework when i left my house .A.is doing B.was doing C.did D.does

问题描述:

he___ his homework when i left my house .A.is doing B.was doing C.did D.does

B
when 引导的状语从句,当一个动作发生时,另一个动作正在进行,根据LEFT 可知主句用过去进行时.