不定式和动名词区别请问不定式和动名词的被动形式和完成形式在使用上有什么区别,什么时候该用哪个,什么时候两个可以互换,请知

不定式和动名词不是动词,没有被动形式和完成形式.他们做主语时是可以互换的.
如：To help him clean the house is difficult .=Helping him clean the house is difficult.
但是to help him clean the house 如果放到后面去用形式主语来代就不可以与后一句互换了.
如：It is difficult to help him clean the house .可以.
而It is difficult helping him clean the house .不可以.