It后不是加to do sth吗?

I find it is easy to do sth 中是to do sth 为什么又有
It isn't easy being the top students in the class。
翻译：做班里拔尖生不容易

后加to do It's time to后一般加什么？ It's time to do sth it's +adj+to do sth It's better to do A than do B It's + adj+to do sth It isn't +adj+to do sth What's that got to do with it? It’s fun to do the impossible.译成中文是? It's not what Oxford is there to do! it`s a bother for you to do this.