He won't go to attend her birthday party unless______.

问题描述:

He won't go to attend her birthday party unless______.
A.invite B.invited C.is invited D.to invite
unless后省略的内容是什么

答案是B
UNLESS invired 在这里是unless(连接词) + 分词结构,等于 unless he is invited (连接词+ 句子)结构.