为了让考研的同学更高效地复习考研英语，新东方在线考研频道整理了考研英语知识点背诵：it 做形式主语，考研的同学可以了解一下，希望对大家有所帮助。
考研英语知识点背诵：it 做形式主语
it 做形式主语
当主语从句处在句首时，有时谓语结构比较短，会形成头重脚轻的句式，不符合英语语言规则，因此可以将主语从句用it替代，而真正的主语从句置于句尾。常见的四种情况是：
（1）It is+名词+主语从句；
eg：It is a pity that you should have to leave.
It is still a mystery what caused the accident.
（2）It is+形容词+主语从句；
eg：It is clear that the whole project is due to failure.
It is certain that he will win the match.
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.
It is important that we all should attend the meeting.
It is strange that the man should have stuck to his silly ideas.
(3) It is+过去分词（said /planed/expected/known） +主语从句；
eg：It is said that President Bush will visit our school next week.
It is known to all that the gun powder was first invented by the Chinese.
It is suggested that the work should be done with great care.
(4) It +系动词+形容词表语形式+主语从句
eg：It seemed certain that he will win the prize.
It happened that the two cheats were there.
以上是新东方在线考研频道为考生整理的“考研英语知识点背诵：it 做形式主语”相关内容，希望对大家有帮助，新东方在线考研频道小编预祝大家都能取得好成绩!更多英语复习相关信息尽在新东方在线考研英语频道。