It's good helping blind people to cross the road.help为什么要用动名词?

It's good helping blind people to cross the road.help为什么要用动名词?
It's good helping blind people to cross the road.
help为什么要用动名词?

It's good helping blind people to cross the road.help为什么要用动名词?
这是固定句型 it is good doing sth表示做某事有益..
帮助盲人过马路是有益的

It is good in doing sth.固定搭配,IN可以省略.

It is good in doing sth.固定搭配,IN可以省略.
in 作为介词,介词后面的动词都要用ing形式.
to 后面有时接 do 而不是doing ,因为那时to不是做介词而是做不定式.