it 代替连词 that 引导的从句作形式主语
例句：It's said that Tom has come back from abroad
It was reported that dozens of children died in the accident .
it 代替连接代词或连接副词引导的从句作形式主语。
例句：It is still a question when we shall have our sports meet .
我们将什么时候举行运动会还是一个问题。
It is uncertain whether he can attend this conference or not .
他能否来开会还不能确定
it
英 [ɪt] 美 [ɪt]
pron.环境;情况,局势;正是所需(要或想望)的事物;〈非正式〉性交;性欲;(儿童游戏中的)捉人者,找人者