as的几种用法：1.做连词，固定搭配as……as，意思是“和……一样”；2.做连词，表示“当……的时候”；3.做连词，表示“因为”4.做连词，表示“尽管”等。

做连词，固定搭配as……as，意思是“和……一样”
例句：

My sister is as tall as me.

我姐姐和我一样高。

He runs as fast as me/I. 

他和我跑得一样快。

She is as beautiful as me/I. 

她和我一样漂亮。

Being a mother isn't as bad as I thought at first!

做一位母亲并不像我当初想的那样糟！

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。

I was always hard up as a student. 

我当学生时总是很拮据。

The crowd cheered as she went up the steps to the bandstand. 

当她走上演奏台的台阶时，人群欢呼起来。

All the jury's eyes were on him as he continued.

所有陪审员的目光在他继续下去时都集中在了他身上。

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。

Enjoy the first hour of the day. This is important as it sets the mood for the rest of the day.

享受一天中的第一个小时。这很重要，因为这第一个小时决定当天其余时间的情绪。

做连词，引导让步状语从句，意思是“虽然，尽管”

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。

Happy as they were, there was something missing. 

尽管他们很快乐，但总缺少点什么。

Much as they hope to go home tomorrow, they're resigned to staying on until the end of the year. 

尽管他们很希望明天就回家，但不得不待到年底。

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。

As Albert Einstein suggested, things should be as simple as possible, but no simpler. 
   
正如爱因斯坦认为的那样，事情要尽可能地简单，而不是简单一些。

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。

Personas are represented as individual people.

作为个体代表的人物角色。

He has worked as a diplomat in the U.S., Sudan and Saudi Arabia.

他曾做过驻美国、苏丹和沙特阿拉伯的外交官。

The news apparently came as a complete surprise.

这消息显然是个彻头彻尾的意外。

I really value him as a friend. 

我真的把他视为好朋友。