I know she won't come to join us unless she ___to.

问题描述:

I know she won't come to join us unless she ___to.
A.tells B.has told C.is told D.told
,为什么?

除非她被(is)要求(told)来参加(to come),这是她被要求干什么,to后面省略了前面的谓语动词come.