It‘s obvious that the earth is round.
It's good that we speak English in English classes.
It's important that students study hard .
It‘s necessary/important that .很重要
It‘s believable/unbelievable that .是可信/不可信的的
It‘s possible/impossible that ...是可能/不可能的
It‘s unimportant that ...是不重要的
It‘s difficult/hard that ...是难的
It‘s helpful that ...
It‘s useful that ...是有用的