问题补充：
— The floor is clean and dry now. Who ?
— Sorry, I don’t know.
A. mopped it up
B. has mopped it up
C. has mopped up it
D. mopped up it
答案：
A. mopped it up
(答案→)B. has mopped it up
C. has mopped up it
D. mopped up it
解析：从题意来讲，本题需要的是现在完成时，而mop ..up 为动词+adv词组，若宾语为人称代词时，位于中间，故选B
