不定式主动代被动的情况?

问题描述:

不定式主动代被动的情况?
比如说,The problems is difficult to slove
到底在什么情况下主动代被动呢?
there be句型呢?

不定式作定语,放在被修饰词后面,与前面被修饰的名词或代词有动宾关系,又在句子中与另一名词或代词有主谓关系,不定式要用主动表被动含义.
I have much work to do. 我有许多要做的事情.(与work有动宾关系,与I有主谓关系)
Tom is looking for a room to live in. Tom在找一间住的房间.(与room有动宾关系,与Tom 有主谓关系)
He has a family to support.?他要维持一个家庭.(与family有动宾关系,与he有主谓关系)