问题补充：
——Catherine, I have cleaned the room for you.
——Thanks, You it. I could manage it myself.
A. needn’t do
B. needn’t have done
C. mustn’t do
D. shouldn’t have done.
答案：
A. needn’t do
(答案→)B. needn’t have done
C. mustn’t do
D. shouldn’t have done.
解析：考查情态动词的完成时表示虚拟的用法：从第一句知道;我已经帮你打扫了房间，可知后面是对过去情况的虚拟，答案在BD里面选，needn’t have done是本不必做而做了，shouldn’t have done.本不应该做而做了，从后面的句子：I could manage it myself.我自己能行，可知选B。
