定语从句与介词的宾语从句——选择题一道.

The newly built cafe,the walls of （）are painted light green,is really a peaceful place for us,especially after hard work.
A what BWhich
疑惑①：答案选B,但是我觉得如果是定语从句,of which 应该放在 the walls前面吧,否则定语从句岂不是无主语?
答 whose walls = of which the walls = the walls of which
定语从句的主语是 the walls of which是定语从句中的定语修饰 the walls
疑惑②：对于A,我只能从语感是觉得无意义,请老师从语法角度,科学地分析不选择A的原因.
答 what只能引导名词性从句 是连接代词 不是关系代词 不能引导定语从句 本句是非限制性定语从句 所以不能用what代替先行词 the cafe 只能用关系代词which 代替the cafe