Everyone knows the answer,---------.反意疑问句.

陈述句部分主语是不定代词everyone,nobody,somebody,someone
时,后反意部分主语用they（当强 调全体时）或he （当强调个体时）.如：
No one knows him,do they?
Someone is waiting for you,isn't he ?
所以此处用it 和they 都是正确的