(4) it ＋过去分词＋从句

    It is reported that…                       据报道…

    It has been proved that…                  已证实…

    3. 主语从句不可位于句首的五种情况

   (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。例如：

       It is said that President Jingo will visit our school next week. (right)

       That President Jiang will visit our school next week is said. (wrong)

   (3) It happens…, It occurs… 结构中的主语从句不可提前。例如：

       It occurred to him that he failed in the examination. (right)

       That he failed in the examination occurred to him. (wrong)

   (4) It doesn’t matter how/whether …结构中的主语从句不可提前。例如：

       It doesn’t matter whether he is wrong or not. (right)

       Whether he is wrong or not doesn’t matter. (wrong)

   (5) 含主语从句的复合句是疑问句时，主语从句不可提前。例如：

       Is it likely that it will rain in the evening? (right)

       Is that will rain in the evening likely? (wrong)

    4. What 与that 在引导主语从句时的区别

    What 引导主语从句时在句时在从句中充当句子成分，如主语．宾语．表语，而that 则不然。例如：

    1) What you said yesterday is right.

      2) That she is still alive is a consolation.

二．宾语从句

宾语从句就是在复合句中作宾语的名词性从句，通常放在主句谓语动词（及物动词）或介词之后。joozone.com