The mother didn't know who to blame for the broken glass.为什么要用 to blame

问题描述:

The mother didn't know who to blame for the broken glass.为什么要用 to blame
为什么不是who was to blame ,而是who to blame ,不是有个短语是 sb be to blame

这里的主语是mother 相当于 mother to blame who ,who是疑问词提到前面.sb be to blame 是被责备的人是主语