His parents found _____

题目

His parents found _____
A.it necessary B.that necessary C.it is necessary D.necessary
我很奇怪,为什么答案是A?C咋地就不可以拉?it...和it is.有什么区别?
后面的是to tell him everything that had happend

答案

A 是对的
found it (形式宾语） adj (形容词作宾补）
C 是从宾语从句里变来的,his parents found that it is necessary ( 后面必须加to do sth)
可见,C,的选项不完整,句子没完