---The answer to the question is very easy,isn't it?---Yes,but I don't think_____ know it.

---The answer to the question is very easy,isn't it?---Yes,but I don't think_____ know it.
A.everybody B.anybody C.somebody D.nobody
选那个?为什么?
如果选A的话，那么know是不是应该用knows？
如果选B的话，不是说anybody用在否定句中就是somebody的变形吗？