问题补充:
all the homework assigned by the school the students have to work at it till midnight
A. Completing
B. To complete
C. Having completed
D. To have completed
答案:
A. Completing
(答案→)B. To complete
C. Having completed
D. To have completed
解析:句意:为了完成学校布置的全部的家庭作业,学生们不得不学习到了午夜。表示目的,为了……,故用不定式,且与谓语动词表示的动作没有时间的先后顺序,故用不定式的一般式,选B。