【题目】—Catherine, I have cleaned the room for you.
— Thanks. You _______ it. I could manage it myself.
A.needn't have done
B.needn't do
C.mustn't do
D.shouldn't have done

【答案】A
【解析】考查固定用法。根据句意可知Catherine对对方为她打扫了房间表示感谢并提到对方本来不必为她打扫房间。很显然对方打扫房间是过去所为，表达“去不必做某事”用needn't have done sth.