4.________ 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 1.________ in the queue for half an hour,Tom suddenly realized that he had left his wallet at home.A.To wait B.Have waited C.Having waited D.To have waited原因说清楚点,我有些笨.

C 动名词做句子主语 。
C 非谓语动词作状语 ，与逻辑意义主语 Tom 是主动关系，同时动作发生在主句之前，所以用现在分词的完成式。

B， 主语是exposing 这件事，而非人， 故排除C和D， 而A的主语则是skin, 所以答案为B

4 C
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）
1 Having waited in the queue for half an hour,Tom suddenly realized that he had left his wallet at home.(分词结构做时间状语)
===After he had waited in the queue for half an hour,Tom suddenly realized that he had left his wallet at home .（时间状语从句）