It+系动词+数词+单位+形容词 造句

it作形式主语可指代动名词短语、不定式短语或从句.
eg: It is a waste of time arguing with him.
It is easy to finish the work.
It is said that he killed his wife.
如果硬要区分不定式和动名词的区别,只能说不定式指偶然性动作,动名词指习惯性动作.it作形式主语或形式宾语时,指代不定式的情况要比指代动名词的情况常见.

1.It is said that 据说（＝people say 即大家都这么说）that 后面接一个从句,that 可省略.例：
It is said （that） he is only 13 years old.据说他才13岁.
=He is said to be only 13 years old.他据说才13岁.
其它几个的用法都是一样.
2.It is thought （that）大家认为.有人认为.that后同样接一个句子.例：
It is thought （that ）he is the greatest person in the world.他被认为是世界上最伟大的人（同样请写出另两种表达）.
3.It is known that 众所周知.
4.It is reported that 据报道.有报道称.
5.It is estimated that 据估计.
6..It is believed that 据信.大家相信.