as的用法：
1、as做介词，意思是“作为”
例句：
French is known as the most beautiful language in the world.
法语以世界上最美丽的语言著称。
2、as做连词，引导时间状语从句，意思是“当……的时候”
例句：
My mother was cooking fish as I arrived home.
当我到家的时候，我妈妈正在做鱼。
3、as做连词，引导原因状语从句，意思是“因为”
例句：
As rain has fallen, the air is cooler.
因为下过雨，所以空气比较凉爽。
4、as做连词，引导让步状语从句，意思是“虽然”
例句：
Young as he is, he has been one of the most famous painters in our country.
虽然他还很年轻，但已经成为我们国家最有名的画家之一。
5、as做连词，引导方式状语从句，意思是“以……方式”
例句：
Do as the Romans do when in Rome.
入乡随俗
6、as做关系代词，引导定语从句
例句：
This is the same game as I played yesterday.
这和我昨天玩的游戏一样。