It's a good time to climb hills中的It是不是形式主语

It's a good time to climb hills中的It是不是形式主语 it's a good time to climb hills 可以等于it's a good time for cli It's a good time to climb hills.(同义句） It's cool.It's good time to climb hills.中的it和to的不定式个在句中做什么成分 It's a long time since i saw you last 这句中的it是不是形式主语? It,s good to live in a neighbourhood like that.it是形式主语吗? 英语语法问题It's not up to me to decide.这句话中的it是不是形式主语? Tom found（）interesting to climb hills为什么不能用it’s? It,s good to live in a neighbourhood like that.it是形式主语吗?这句话的 比如it must be obvious中的it就是形式主语那么it is good也是形式主语吗?如何区分it是不是形 It's been a long time.^^ I've learned to rock climb. It is fun _(climb) hills