It was required by the headmaster that all the students at the meeting.A. should presentB.

问题补充：

It was required by the headmaster that all the students at the meeting.

A. should present

B. present

C. attended

D. be present

答案：

A. should present

B. present

C. attended

(答案→)D. be present

解析：考查虚拟语气。require要求，从句用should + v原形的虚拟语气，should可以省略。be present at出席，根据句意选D。