It's a fun to do sth.fun是不可数名词为什么还要加a?

It's fun to do sth.中的fun什么词性 It's a fun to do sth.fun是不可数名词为什么还要加a? it is a great fun to do sth.还是it is great fun to do sth It' fun to do sth 这句有没语法错误,It's+ adj 后面什么时候加to do sth 什么时候doing sth It is great fun to do ...It is great fun to do sth还是It is a great fun to do sth? It is fun to do sth造句 It is fun to do sth.造句. It's fun 后面是跟doing sth.还是跟to do sth. what a fun和how fun的用法是what a fun it is to do sth还是how fun ? it is +形容词+to do sth ,为什么有些资料上是it's fun +to do sth,fun是形容词吗 It is fun to do sth对,还是It is fun to doing sth It's fun to do sth.是将动词不定式做了主语,那么该动词不定式能改成动名词吗,为什么?因为It's fun to do sth=To do sth is fun.那么有没有It's fun doing sth呢?另外，Eating food is good for your health能不能改为It' what great fun it is+to do sth 吗 It's a good idea to do sth.造句 It's a good idea to do sth It’s fun to do还是doing it's a time to do sth 和it's time to do sth 有什么区别 It is fun?到底是It is fun to do sth 还是It is fun doing sth?It is fun for sb +