what只用于宾语从句中．（先行词是动词）
that which 可以用于定语从句中．（先行词是名词）
这道题应该要选C吧?
PS.
介词+疑问代词=疑问副词.其中是因为从句中的介词提前,所以有这种情况.e.g：I may have to to into hospital,in which case I won't be going on holiday.我可能得住院,如果那样我就不去度假了.
关于地点的不知道这句行吗：
I would like to go to the place where I can see the beach.