-- is that used for?
--- the floor.
A. Why; To cleaning
B. What; Cleaning
C. Why; To clean
D. What; clean
网友回答
A. Why; To cleaning
(答案→)B. What; Cleaning
C. Why; To clean
D. What; clean
解析：句意“这是用来干什么的？”“扫地。”所以第一个空选what。第二空应该做介词for的宾语，所以使用cleaning。答案B。