谁来帮我分析一个高中英语句子

题目

谁来帮我分析一个高中英语句子
The mother didn't know who to blame for the broken glass as it happened while she was out.
who为什么不能改为whom?blame为什么没有使用被动结构?
句子中缺少的不是宾语吗?为什么是缺少主语?

答案

这是宾语从句的缩略句型,很常见. 常用于know, teach, learn, expect, think 动词后.
以疑问词+to do的结构出现.
如: I don't know how to do it.
相当于: I don't know how I should do it.
所以这句话也相当于:The mother didn't know who should be to blame for the broken glass as it happened while she was out.
WHO 在这个宾语从句中充当主语. sb be to blame.这是个句型. 不能用whom