1．作人称代词
John likes playing Pingpong./ He always does it in the afternoon.(指代上下文提到的事物)/It's time we went home./ How far is it from here to your home / It is getting warmer and warmer./ It's very quiet at the moment.(可指时间、天气、环境等)
2．作形式主语,代替由不定式、动名词或从句表示的真正主语.
It's important for us to learn a second language./ It's no use talking to him./ It's known to all that the earth goes round the sun.
3．作形式宾语,代替由不定式、动名词或从句表示的真正宾语.
We feel it our duty to help others./ He made it clear that he would leave the city.
4．表示“喜欢、恨”等心理方面的动词后面接it,构成固定结构,这类动词有enjoy,prefer,love,like,hate,dislike,appreciate等.
I’d appreciate it if you would like to teach me how to use the computer.如果你教我如何使用电脑我感激不尽.
强调结构：It is (was) ＋被强调部分＋that (或who)．..
注意：在强调结构中,如被强调部分为时间状语或地点状语,应用that .在复习中,一定要注意句式的不同.
It was in Shanghai that I bought the guitar.(that引起强调句)
It was Shanghai where I bought the guitar.(where引起定语从句)
It was twelve o'clock when we arrived there.(when引起时间状语从句)
It was at twelve o'clock that we arrived there.(that 引起强调句)
