问题描述：
As it turned out to be a small party,we____so formally
答案是选“need't have dressed up'
为什么不选 did not need dress up ,如果在need后加上to可以选吗?
答案是选“need't have dressed up'
为什么不选 did not need dress up ,如果在need后加上to可以选吗?
问题解答：
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