【题目】—What are they _______? ( )
—They are _______ the windows.
A.doing; clean B.doing; cleaning C.do; clean
【答案】B
【解析】
句意:—他们正在干什么?—他们正在擦窗户。考查了现在进行时的用法,其结构为主语+be+动词现在分词,clean现在分词cleaning,故选B。

【题目】—What are they _______? ( )
—They are _______ the windows.
A.doing; clean B.doing; cleaning C.do; clean
【答案】B
【解析】
句意:—他们正在干什么?—他们正在擦窗户。考查了现在进行时的用法,其结构为主语+be+动词现在分词,clean现在分词cleaning,故选B。