as的用法：
1、as做介詞，意思是“作為”
例句：
French is known as the most beautiful language in the world.
法語以世界上最美麗的語言著稱。
2、as做連詞，引導時間狀語從句，意思是“當……的時候”
例句：
My mother was cooking fish as I arrived home.
當我到家的時候，我媽媽正在做魚。
3、as做連詞，引導原因狀語從句，意思是“因為”
例句：
As rain has fallen, the air is cooler.
因為下過雨，所以空氣比較涼爽。
4、as做連詞，引導讓步狀語從句，意思是“雖然”
例句：
Young as he is, he has been one of the most famous painters in our country.
雖然他還很年輕，但已經成為我們國家最有名的畫家之一。
5、as做連詞，引導方式狀語從句，意思是“以……方式”
例句：
Do as the Romans do when in Rome.
入鄉隨俗
6、as做關系代詞，引導定語從句：
例句：
This is the same game as I played yesterday.
這和我昨天玩的游戲一樣。