(·成都一模) all the homework assigned by the school the students have to work at it till

问题补充：

(·成都一模) 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：选B考查非谓语动词。此处为目的状语， 因此使用不定式，排除A和C，而且不强调完成，因此使用不定式的一般式，故选B。