很多位置都可以
一.作主语
Walking is a good exercise for both young
二.作宾语
We enjoy swimming very much.
三.作宾补
We saw them walking across the road.
四.作表语
His hobby is collecting stamps.
五.作定语
Do you know the boy lying under the big tree?
六.作状语
Looking out of the window,I saw many green trees.