请教这题英语选择题为什么会选CThis is a very difficult operation. It is essential that you _____ for emergency.A. are to be preparedB. would preparedC. be preparedD. must be prepared
问题描述：
请教这题英语选择题为什么会选C
This is a very difficult operation. It is essential that you _____ for emergency.
A. are to be prepared
B. would prepared
C. be prepared
D. must be prepared
答
该题考点：1、被动语态；二、省略
该句完整形式是
It is essential that you should be prepared for emergency.
该句还用到倒装，原语句为
That you should be prepared for emergency is essential .
答
是虚拟语气的用法之一吧.essential后要接动词原形