一般情况是：不定式和动名词都可以在句中作主语，但下面一些词的后面一般用doing，如hopeless,useless,no use,no good等等。大多还是用to do作主语。
It is + no use,no good (fun,a great pleasure,a waste of time,a bore等名词）+doing sth.
t is no use crying.哭没有用。
It is no good objecting.反对也没有用。
It is a great fun playing football.打篮球很有趣。
It is a waste of time trying to explain.设法解释是浪费时间。
It is + useless (nice,good,interesting,expensive等形容词)+ doing sth.
It is useless speaking.光说没用。
It is nice seeing you again.真高兴又遇到了你。
It is good playing chess after supper.晚饭后弈棋挺好。
It is expensive running this car.开这种小车是浪费。
