约1640字。

　　As的用法
　　（一） as作连词的用法:
　　1.作“在。。。期间，当。。。的时候”引导时间状语从句. as与when，while都是引导时间状语从句的从属连词，含义都是"当……的时候"。但它们有区别：用when时，从句的动作可以与主句的动作同时发生，也可以先于主句的动作发生；用while时，从句的动作为一过程，主句动作与从句动作同时进行或在从句动作过程中发生；用as时，主句和从句的动作同时发生，具有延续的含义。
　　①下列情形时,只用as, 而不用when或while。
　　1)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 sings as she goes to school.
　　He looked behind occasionally as he went forward in the forest.
　　2)表示两个同步发生的动作或行为,意思是随着-----的发展.如:
　　As time went on / by, she bee more and more beautiful .
　　As children get older, they bee more and more interested in everything.
　　3)表示两个短暂行为或事情几乎同时发生.如:I watched her as she read the book.
　　I thought of it just as you opened your mouth.
　　Just as the flying worm hit her face, she gave a loud cry.
　　4)接在名词后面表示某一个年龄段时.如:
　　As a young man, he was active in sports.
　　②when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 I was at college, I could speak several foreign languages. When the clocck twelve, I had slept for 2hours.
　　③ 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.
　　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 he’s been ill for ages, I will help him.
　　As / Since you're not feeling well, you may stay at home.
　　As he wasn't ready , we went without him.
　　as，because，since都可以表示因果关系，连接原因状语从句，含义是因为，由于，但它们有区别：because表示的语气最强；as一般放在句首，语气较弱，较口语化；since常常用在书面语中，表示多为对方已知的、或稍加分析便可得知的原因，有时可译作"既然"。
　　3. As =in the way that作"像"、"按照……的方式"解,引导方式状语从句。如:
　　Do as I told you.    Remember, you must do everything as I do.
　　4. 用于as--- as或not / so/ as ---- as中,前一个as是副词,后一个as是连词,引导比较状语从句。as...as意为"和……一样"，表示同级的比较。使用时要注意第一个as为副词，第二个as为连词。其基本结构为：as+ adj./ adv. +as。其否定式为not as/so +adj./ adv. +as若有修饰成分，如twice, three times, half, a quarter等，则须置于第一个as之前。如:They helped the old as much as possible.
　　I don't speak English so/ as well as she does.
　　几个关于as...as的常见句型：
　　(1)as...as possible