as可以作连词、介词及关系代词和副词。现将其用法小结如下:
（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.注意与when、 while的用法区别。
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 became more and more beautiful .
As children get older, they become 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 clock struck 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.
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。如:They helped the old as much as possible.
I don't speak English so/ as well as she does.
5. 表示虽然,尽管 等,引导让步状语从句,常用倒装语序,模式为:
adj. /adv. / n.+as +主语+谓语+主句。如: Young as he is, he knows much.
Tired as they were, they walked on.
6. 表示也------一样。 She is a doctor, as was her husband.
（二）、 as作关系代词,引导定语从句,表示正如,这一点.如:
He is very careful, as we all know.
As is well-known, Taiwan belongs to China.
另外,当先行词被the same, such等词修饰时,常用as来引导定语从句。如:
Such a clever girl as she can learn anything quickly.
I was reading the same book as he bought yesterday.
（三）、as作介词的用法.
1.表示好像。如:He dressed as a policeman.
2. 表示作为当作。如：I found a job as a guide.
3. 当某人是某身份时。如：As a child , she was sent to abroad.
4. as引导的介词短语大多用作状语,as译为"作为";少数情况可引起宾语补足语。如:
As a Party member, I'll take the lead in everything. (状语)
She works as a model. (状语)
She has me as one of her best friends.(引起宾语补足语)
（四）、作副词的用法 1 表示与------等同。如：This dress is twice as expensive as that one. 2 像，如等。如：As before, he remained unmoved.
总之，通过以上的分析，我们对as的词性和用法有了比较全面的理解和把握，才能在实际的运用中做到心中有数，应付裕如。
生词表:
（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.注意与when、 while的用法区别。
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 became more and more beautiful .
As children get older, they become 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 clock struck 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.
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。如:They helped the old as much as possible.
I don't speak English so/ as well as she does.
5. 表示虽然,尽管 等,引导让步状语从句,常用倒装语序,模式为:
adj. /adv. / n.+as +主语+谓语+主句。如: Young as he is, he knows much.
Tired as they were, they walked on.
6. 表示也------一样。 She is a doctor, as was her husband.
（二）、 as作关系代词,引导定语从句,表示正如,这一点.如:
He is very careful, as we all know.
As is well-known, Taiwan belongs to China.
另外,当先行词被the same, such等词修饰时,常用as来引导定语从句。如:
Such a clever girl as she can learn anything quickly.
I was reading the same book as he bought yesterday.
（三）、as作介词的用法.
1.表示好像。如:He dressed as a policeman.
2. 表示作为当作。如：I found a job as a guide.
3. 当某人是某身份时。如：As a child , she was sent to abroad.
4. as引导的介词短语大多用作状语,as译为"作为";少数情况可引起宾语补足语。如:
As a Party member, I'll take the lead in everything. (状语)
She works as a model. (状语)
She has me as one of her best friends.(引起宾语补足语)
（四）、作副词的用法 1 表示与------等同。如：This dress is twice as expensive as that one. 2 像，如等。如：As before, he remained unmoved.
总之，通过以上的分析，我们对as的词性和用法有了比较全面的理解和把握，才能在实际的运用中做到心中有数，应付裕如。
生词表:
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