---Catherine,I have cleaned the room for you.
问题描述：
---Catherine,I have cleaned the room for you.
---Thanks.You______ it.I could manage it myself.(2005福建)
A.needn’t do
B.needn’t have done
C.mustn’t do
D.shouldn’t have done
为什么选B,不选A?
答
因为房间已被打扫了,所以用现在完成时.