英语 过去分词 Exposed to sunlight for too much time will do harm to one's skin.其中 Exposed 作什么成分 .可是过去分词不是不能作主语吗?

Exposed是条件状语，过去分词主要有两种意思，一是表被动，二是表完成。
If you are exposed to sunlight for too much time ,it will do harm to you skin.

Exposed是条件状语，过去分词主要有两种意思，一是表被动，二是表完成。
如compared with在句首 compared是一个用法
Exposed to sunlight for too much time看做一个整体，做主语。

Exposed to sunlight too much time 是句子的主语

Exposed to sunlight for too much time看做一个整体，做主语。或者这里的Exposed应该改为Exposing。

（Exposed to sunlight for too much time）括号部分为该句子的主语 will do harm to one's skin.这句话还可以说成“It's harm to one's skin when sb.is exposed to sunlight for much time”...

Exposed to sunlight for too much time是主语。