2.作句子的形式主语，代替不定式、动名词或从句。

　　It took me five minutes to finish reading the exercise.

　　It cost me five yuan to buy the pen.

　　The color TV set costs me more than 2，000 yuan.

　　I spent ten hours in finishing the work.

　　I spent twenty yuan on the shirt.

　　It is no use crying now. You'd better study hard now.(it is no use doing sth. )

　　To his surprise， it turned out that Tom failed the entrance examination.(to one's surprise 使某人感到惊奇)

　　It's a pity that you didn't watch the match.

　　It is necessary for us to have some exercise every day.

　　3.作句子的形式宾语，代替不定式、动名词或从句。

　　They all regard it their duty to help the poor people.

　　I don't think it worthwhile taking so much trouble.(It's worthwhile doing. 做……事是值得的)

　　We find it difficult to learn English without practicing.

　　I don't think it very important that we should take part in the discussion.(take part in 参加)

　　4.构成强调句型。当强调的部分是主语，并且主语是人时，句型中的that 也可以换作who.

　　强调句基本构成 it is that…

　　It is in the room that we met each other for the first time.

　　It was not until 1936 that basketball became a part of the Olympic Games.(not until 直到……才)

　　It was they who attended the meeting last week.

　　It is because the book is so useful for my work that I bought it.