Mrs Smith spoke loud enough for everyone in the class to hear_____

问题描述:

Mrs Smith spoke loud enough for everyone in the class to hear_____
为何句末不用加it,而是什么都不填?

Hear 可以用作不及物动词,就这么简单.
如果非要加宾语,也不是it,这句的情况应该是...to hear what he said.