I sent an MP4 to Alice by mail just now.You___so.She is coming tomorrow

题目

I sent an MP4 to Alice by mail just now.You___so.She is coming tomorrow
A.needn't do
B.needn't have done
C.musn't do
D.musn't have done

答案

B
needn't have done sth 表示过去没必要做什么,而事实上已经做了