in the regulations that you should not tell other people the password of your e-mail account.
A. What is required
B. What requires
C. It is required
D. It requires
网友回答
A. What is required
B. What requires
(答案→)C. It is required
D. It requires
解析：句子中的it是形式主语，代替后面由that引导的主语从句。require的宾语从句中要用虚拟语气，It is required 后接的主语从句中也要用虚拟语气，即should加动词原形。