eg：China is no longer what she used to be.
The question is who is responsible for what has happened.
eg：That the college will take in more students is true.
Whether he will come or not hasn't been decided.
Why he isn't here is not clear to everyone.
eg：It is a pity that you should have to leave.
eg：It is clear that the whole project is due to failure.
如果是It is necessary/important/strange/natural+that引导的主语从句，从句中的谓语动词一定要用should+动词原形;
eg：It is necessary that one should master the skills of operating computer.
(3)It is+过去分词+主语从句;It is said/planted/expected…
eg：It is said that President Bush will visit our school next week.
eg：It seemed certain that he will win the prize.