核心问题
As it turned out to be a small house party, we ____ so formally.
A. needn't dress up B. did not need have dressed up
C. did not need dress up D. needn't have dressed up(全国研考,98-2)
《历年英语考研试题精解及模拟试题》(中国人大出版社，p.31)对上题做了如下解答：
“‘needn’t have dressed up’意为‘本来用不着穿得衣冠楚楚’带有虚拟的含义，这符合题意，故应选D。”
请问 needn't have dressed up 带有虚拟含义吗?
词典解答
应当搞清楚,needn't have done 结构并不是虚拟语气,也不与表示虚拟条件的状语连用。它的真实意义是“本不必做某事”。
[试题句意]原来是一个小型的家庭晚会,我们本不必穿得那么正式。