if,when,which难题

Do you know ___________?

A.if it will be fine tomorrow. B.where did they see her.
C.when shall we have a picnic. D.which would you like.
并请说明原因

which&when when 与which 区别? when 和if which direct when you sleep if和when的区别 where,in which,when,on which有什么区别? What How When Who Which Where Does 定语从句WHEN与WHICH的区别 定语从句中`when与on which while,which,unless,when 选哪个？