Being exposed to sunlight for too much time will do harm to one's skin

问题描述:

Being exposed to sunlight for too much time will do harm to one's skin
A.Exposed B.Having exposed C.Being exposed D.After being exposed
为什么ABD不行

动名词作主语,其它不是.为什么一定要动名词动名词可以作主语,其它几个选项不可以做句子主语。