Being exposed to sunlight for too much time will do harm to one's skin.(动名词结构做主语)
==When you are exposed to sunlight for too much time,it will do harm to your skin.（时间状语从句）

主语是being exposed to sunsunshine,谓语是will do harm to,宾语是skin,for too much time是定语.

皮肤被晒伤,所以选择被动,所以是B或者D.但是D不能做主语,因为它前面是个介词,所以只能做状语.您好。形容词是不是不能作主语？比如exposed？