1.选 C,what = the way (that) ；which引导名词性从句表示的是“哪个”,当然不能用在这里
2.选 D,from which she had come是定语从句,修饰the direction,先行词which指代the direction,也就是she had come from the direction.她从她来的方向跑回
3.those后的who,当然不能省,这里those是先行词跟在than后面作比较的对象,who don't是个省略的定语从句修饰those,who在定语从句里作主语,不能省略
4.赞同你的意见,选D which引导非限制性定语从句,在从句中作主语.如果不选D,我怀疑答案有问题.