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。