—Must we keep the room all the time? —No you don’t have to. A. cleaningB. cleanedC. to cl

问题补充：

—Must we keep the room all the time?

—No, you don’t have to.

A. cleaning

B. cleaned

C. to clean

D. clean

答案：

A. cleaning

B. cleaned

C. to clean

(答案→)D. clean

解析：keep sb/sth +adj让某人或某物保持某种状态。根据句意：我们必须一直保持教室干净吗？--不，你不必。 keep the room clean让教室保持干净，故选D。