“as”是英语中的一个常用词，它有多个用法和含义。以下是一些“as”在英语中的主要用法：
引导时间状语从句：当“as”引导时间状语从句时，表示“当……的时候”。
复制
When she was young, she would sing as she played the piano.
引导原因状语从句：“as”也可以引导原因状语从句，表示“因为”。
复制
As it was raining, we stayed indoors.
引导让步状语从句：“as”还可以引导让步状语从句，表示“尽管”。
复制
Weak as she is, she still insists on doing exercise.
连接并列句：在并列句中，“as”可以用来连接两个并列的句子。
复制
She is a good student, as her parents always expected.
表示“像……一样”：“as”还可以用来表示“像……一样”。
复制
She sings as sweetly as a bird.
引导同位语从句：在某些复杂的句子结构中，“as”可以引导同位语从句。
复制
The news that the project was canceled came as a surprise to everyone.
表示“正如……所知”：“as”还可以用来表示“正如……所知”。
复制
As you know, we will have a meeting next week.
用于比较结构：“as”也经常用于比较结构中。
复制
She is as tall as her father.
表示“按照”：“as”还可以表示“按照”。
复制
Do it as I showed you.
引导状语从句中的省略：在某些情况下，“as”可以引导状语从句并省略某些部分。
省略主谓结构：在这种结构中，“as”前通常有一个分词短语，后面跟着“as”。这种结构中的主谓部分通常可以省略。
省略状语：有时，“as”可以省略整个状语部分，只留下一个名词短语。这种情况通常出现在并列句中。
一、 as作连词的用法:
1. 作"当……的时候",引导时间状语从句。注意与when、 while的用法区别。
① when作"当……的时候"解,可以指较短的(一点)时间,也可指一段时间。如:
When he was at college, he could speak several foreign languages.
When the clock struck twelve, all the lights in the street went out.
② while常表示一段较长的时间或一个过程,强调主句谓语动词与从句谓语动词同时发生。如:
Work while you work. Play while you play.
③ 但属下列情形时,只用as, 而不用when或while。
A) 用于表示同一个人的两种动作交替进行,指"一边……,一边……"。如:
The girl dances as she sings on the stage.
He looked behind from time to time as he went forward.
B)表示两个同步发展的动作或行为,译为"随着……"。如:
As time went on / by, she became more and more worried.
As children get older, they become more and more interested in the things around them.
C)表示两个短促行为或事件几乎同时发生。如:
I thought of it just as you opened your mouth.
Just as the flying worm hit her face, she gave a loud cry.
D) 后接名词表示某一年龄段时,用as。如:
As a young man, he was active in sports.
2. as=since, 作"既然"、"由于"解,引导原因状语从句,常用来表示已为人们所知或显而易见的原因或理由。如:
As / Since you're not feeling well, you may stay
