本讲所归纳的it-句型包括it做形式主语的三中句子：
- it没有具体意义，表示气候、天气、温度、时间、地点、距离等，比如以下句子:
It is very warm and wet in South China these days; it is very cold today;
It's about 2 o'clock now; it's two miles to the nearest police station from here.
口语使用高频
- it充当形式主语或形式宾语
It's illegal to drive without a license; It's pleasant meeting you here in Taiyuan. 口语实用高频
- 强调句，结构为It be的一定形式 中心成分 that/who-分句
It was Doctor Nan-Shan Zhong that/who had contributed a lot to the control of this pandemic. 写作使用高频
