in the school regulations that students should not wear long hair or jewels.
A. It is required
B. What is required
C. What requires
D. It required
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(答案→)A. It is required
B. What is required
C. What requires
D. It required
解析：句意：学校制度规定学生不允许留长发和戴首饰。这里It是形式主语，真正的主语是that引导的从句，主语与require之间是被动关系，故选A。