高二英语The mother didn't know（）is to blame for the broken glas

问题描述：

高二英语The mother didn't know（）is to blame for the broken glass as it happened
The mother didn't know（） is to blame for the broken glass as it happened while she was out.
[ ]
A.who
B.when
C.how
D.what
请解释为什么是A?为什么其他选项是错误的?

1个回答分类：英语 2014-10-14