Teachers required that all the students their homework all alone.A. must finishBwould

问题补充：

Teachers required that all the students their homework all alone.

A. must finish

Bwould finish

C. had to finish

D. finish

答案：

A. must finish

B. would finish

C. had to finish

(答案→)D. finish

解析：考察虚拟语气。Require后面的宾语从句使用虚拟语气should do;should可以省略。故D正确。