它在名词从句中形成主语

它被用作形式的主语早期湮灭，形式的对象的使用。

它被用作更改祝贺信息的形式。

1.很遗憾他犯了这个错误。

that he made such a mistake is a pity .

it is a pity that he made such a mistake.

it is well known/reported/ thought/said that…

it is clear/necessary/certain/true that…

it is a pity/a shame/an honor that…

是否......

it seems that…

1.__is known to all,taiwan is only part of china.

这个网站上一定写了一个错误。

1.基本用法。

当不定式、动名词、从句等用作主语时，避免头重脚轻，通常在句子开头使用正式主语，并将真正的主语放在句子的末尾：

is it necessary to tell his father everything?有必要为这一切起诉他的父亲吗？

it’s no good sitting up too late.熬夜没有任何好处。

it is quite clear that he has read the book.显然，他读了这本书。

it doesn’t matter what he says.他说什么并不重要。

2.几种特殊形式的主题。

用作动词的主语 look、seem、appear、happen、occur、follow 等（后跟该从句或好像从句）：

it seems as if it is going to rain.看起来要下雨了。

it seems that he knows everything.他似乎什么都知道。

from this witness it follows that he must be guilty.从证人的证词来看，他被判有罪。

当领带表结构后面跟着一个由if或when绘制的状语从句时，通常在领带表结构之前使用正式主语来表示说话者对某种情况的看法：

it was a great surprise to me when he did a thing like that.我很惊讶他这样做了。

it would be a tragedy if anything went wrong.如果发生什么事，那就是一场悲剧。

它用于其他固定的句型，例如，如果它不是用于......（如果不是因为），是时候了......（这。等等。