There are said to be two expert doctors attending on the wou

There are said to be two expert doctors attending on the wounded soldier.几道关于非谓语动词的题目
1.There are said to be two expert doctors attending on the wounded soldier.
在这句话中为什么要用attending on,而不用 to attend?
2.attend on 与attend to的关系?相等?
3.The soil was washed away by the flood,exposing bare rock.
为什么expose用现在分词?
Exposed to sunlight for too much time,the color of the curtain faded.
为什么exposed用过去分词?不是be exposed?和be dressed in、 be faced with 等等有什么相同之处?
Being exposed to sunlight for too much time will do harm to one’s skin.
为什么expose用动名词被动形式,为什么去掉Being exposed后说改句缺少主语?

1.attending on 是ing形式做后置定语表当时的状态,不定式做定语表尚未发生、将要进行的动作而不符合该句意排除.
2.attend on(upon)意为照顾、侍候.而attend to 不仅有照看、照料之意,还有处理,办理和注意倾听之意.如:Business has to be attended to; You must attend carefully to these instructions.
3.exposing bare rock 是ing形式做定语,与所修饰的词the flood 构成主谓关系,意为使光秃秃的岩石暴露出来,故用ing形式即现在分词做后置定语.
exposed to sunlight for too much time是ing形式做原因状语,与句子主语the color of the curtain 构成动宾关系,故用ing形式即现在分词做状语.
be exposed to 与 be dressed in 、be faced with 可以看作过去分词做表语表示句子主语的状态.
being exposed to sunlight 是动名词一般式的被动形式做主语,去掉句子不仅结构不完整,意思也不明确.
3.