为什么这句里的be动词用原型?

问题描述:

为什么这句里的be动词用原型?
句子是这样的:
whether it necessary that it (be) as bad as it is.
(这种糟糕是否有必要呢?)
句子里的那个be为什么是原型呢!

例如We never doubt whether it (is) necessary that it (should) be as bad as it is.此时为省略should 的用法,还有很多是这样,比如it is important\strange\necessary that sb (should) do.再比如suggest require ...