① It adj that 从句(大多数情况下that从句后用should 动词原形) Adj: necessary right clear unlikely strange obvious natural important Eg: It is necessary to learn English well. ② It 系动词 名词 that 从句 Non: a pity an honor good news a wonder a fact no wonder no surpeise Eg: It is a fact that you are a good boy. ③ It be 过去分词 that从句 过去分词：said / heard/ reported/ told/ decided/suggested/thought/considered/ hoped/ announced Eg: It is announced that the plan has been canceled. 注意： It be suggested/ advised/ ordered/ requested/ insisted/ demand that从句， that从句要用should 动词原形，should可以省略。 Eg: It is suggested that you (should ) spend more time in studying English . 当suggest表示“表明”时，不可以用虚拟语气 Eg: It suggests that you are an honest boy. Insist 表示“坚持某种说法（事情已经发生过了）”，不用虚拟语气。 表示“坚持要做（事情没有发生）”，要用虚拟语气。 Eg: she insisted that I have never done such thing . She insisted that I study abroad. ④It 动词（ 宾语或状语） that 从句 动词如： appear(显得)/ happen(碰巧)/ matter(重要)/ occur(出现)/ turn out(结果是) Eg: It happened to me that I was away when he came.主语从句不可位于句首的五种情况： 注意： （1）if 引导的主语从句不可居于复合句句首。 （2）It is said /reported?结构中的主语从句不可提前。 正确表达：It is said that President Jiang will visit our school next week. 错误表达：That President Jiang will visit our school next week is said. （3）It happens/occurs?结构中的主语从句不可提前。 正确表达：It occurred to him that he failed in the examination. 错误表达：That he failed in the examination occurred to him. （4）It doesn’t matter how/whether ?结构中的主语从句不可提前。 正确表达：It doesn’t matter whether he is wrong or not. 错误表达：Whether he is wrong or not doesn’t matter. （5）含主语从句的复合句是疑问句时，主语从句不可提前。 正确表达：Is it likely that it will rain in the evening? 错误表达：Is that will rain in the evening likely?