—Must we keep the window all the time? —No you don’t have to. A. openingB. openedC. to o

问题补充：

—Must we keep the window all the time?

—No, you don’t have to.

A. opening

B. opened

C. to open

D. Open

答案：

A. opening

B. opened

C. to open

(答案→)D. Open

解析：句意：我们必须一直开着窗户吗？--不，不必。Keep sth/sb adj保持……，这里需要填写形容词，所以填写open。故选D.