How dirty the windows are! They really require .A. to cleanB. being cleanedC. to have clea

问题补充：

How dirty the windows are! They really require .

A. to clean

B. being cleaned

C. to have cleaned

D. cleaning

答案：

A. to clean

B. being cleaned

C. to have cleaned

(答案→)D. cleaning

解析：考查动词用法。require doing = require to be done需要（被）做，根据句意选择D。