in the school rules that boy students should not wear long hair.
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：考查名词性从句。it是形式主语，that引导的从句是真正的主语。