【规则提炼】代词it常用作人称代词和非人称代词。
　　1. 用作人称代词，代替事、物或人等。
　　①用来指代动物或无生命的事物。例如：
　　Look at the koala. It is very cute. 看这只考拉，它很可爱。
　　②用来指代不清楚性别的小孩或不明身份的人。例如：
　　Someone is knocking at the door. Please go and see who it is. 有人在敲门，去看看是谁。
　　③用来指代前面提到过的事物。例如：
　　I can’t find my pen. I think I must have lost it. 我找不到我的钢笔了。我想一定把它弄丢了。
　　2. 用作非人称代词。
　　①指代时间、日期、天气、温度、距离等。例如：
　　It’s windy today. 今天天气多云。
　　②用作形式主语，指代动词不定式或从句。it作形式主语，常用于下列句型中。例如：
　　It is 形容词 （of/ for... ） to do sth.
　　It is necessary for us to learn English well. 对于我们来说，学好英语很有必要。
　　It takes sb. some time to do sth.
　　It took me fifteen minutes to work out this math problem. 我花了15分钟解决这道数学题。
　　It is said/ reported/ ... that从句
　　It’s said that Jay Chou will come to our city next month. 据说周杰伦下个月将来我们城市。
　　③用作形式宾语，常见于“主语 think（s）/ find（s） it easy/ difficult/ hard/ ... to do sth.”句型中。例如：
　　I find it easy to solve the problem. 我发现解决这个问题很容易。
　　【牛刀小试】
　　Ⅰ. 根据中文意思完成下列句子。
　　1. 门外有个人，我不知道那会是谁。
　　There is somebody outside the door. I don’t know ________________________.
　　2. 从我家到学校8公里。
　　________________________ from my home to my school.
　　3. 解决雾霾问题需要花很长时间。
　　________________________ to solve the problem of haze.
　　4. 据说他下个月要去北京。
　　________________________ he will go to Beijing next month.
　　5. 我发现学好英语很容易。
　　I ________________________ English well.
　　Ⅱ. 同义句转换，每空一词。
　　1. There was a heavy snow last night.
　　________ ________ ________ last night.
　　2. The village is about half an hour’s walk from the town.
　　________ about half an hour’s walk from the town ________ the village.
　　3. We haven’t seen each other for two years.
　　________ has been two years ________ we saw each other last time.
　　4. I think the problem is difficult to deal with.
　　I think ________ difficult ________ ________ with the problem.
　　5. People believe that the rocks have been here for over two million years.
　　________ ________ ________ the rocks have been here for over two million years.