Faced with this problem,i feel so puzzled；像这里ed的作状语,可以还原
i am faced with.一般可以搭配的.
Faceing this problem,i feel so puzzled；表同时进行的动作,强调这个动作正在发生；
to do 一般表示目的,义务做的事,有时也是固定搭配
To help others is our duty；不表同时进行时，什么情况用doing？句子成分中作主语 用doing结构举个例子好吗》、？Watching TV is very interesting ,