问题补充：
As it turned out to be a small house party, we so formally.
A. needn’t dress up
B. shouldn’t dress up
C. were not necessary to dress up
D. needn’t have dressed up
答案：
A. needn’t dress up
B. shouldn’t dress up
C. were not necessary to dress up
(答案→)D. needn’t have dressed up
解析：考查虚拟语气。根据As it turned out to be中的过去时，说明这是与过去的事实相反的虚拟语气，故使用“情态动词+have done”的形式。Needn’t have done本不需要做某事实际上却做了。句意：正如结果所显示的那样，这是一个小型的家庭聚会，我们本不必要穿得如此的正式的。故D正确。
