This is the room whose windows open to ___ south.

应该选A. This is the room whose windows open to the south. 这件房子的窗户面朝南.
此处的south是名词,the south “南方,南部",属于固定用法.上个句子也可以这样讲：
This is the room whose windows faces south. 此处的south是形容词,表示“向南,朝南”,作为动词face的宾语.句式结构可以不用理解的这么透彻.