I couldn't understand( ) the baby alone.

问题描述:

I couldn't understand( ) the baby alone.
A.why she left B.why did she leave C.why had she left
D.why she had left

A、 D正确
从句后要用陈述语序
B、C后都不是
D 表示的是过去完成时 (had+动词过去分词)