they have discussed it for days,but when and where to hold the New Year's party still ___yet.A haven't been decided B hasn't been decided答案是B,我选A了.为什么谓语动词用单数啊?

they have discussed it for days,but when and where to hold the New Year's party still ___yet.A haven't been decided B hasn't been decided答案是B,我选A了.为什么谓语动词用单数啊?
they have discussed it for days,but when and where to hold the New Year's party still ___yet.
A haven't been decided
B hasn't been decided
答案是B,我选A了.为什么谓语动词用单数啊?

they have discussed it for days,but when and where to hold the New Year's party still ___yet.A haven't been decided B hasn't been decided答案是B,我选A了.为什么谓语动词用单数啊?
when and where to hold the New Year's party是后一个句子的主语,这里是不定时的复合结构,作主语时,谓语动词用单数形式