在英语里“up”的用途极为广泛；它是副词虚助词，也是介词，词义不止一个。

　　一、用作介词。例如：

　　（1） As the new manager of the company, Wilcox assured the staff that he would work for the benefits of the company.
　　（2） The scenery here is beautiful as a picture.

　　二、用作表示“程度”的副词。例如：

　　（3） You have performed well. Other students' performance is as good.

　　三、用作从属连词，引导“比较”副词从句。例如：

　　（4） The friendship between us is as strong as a rock.
　　（5） Can our runners run as fast as they used to?

　　四、用作从属连词，引导“时间”副词从句。例如：

　　（6） As the new teacher entered the classroom, the pupils clapped their hands.
　　（7） Alex caught sight of Nancy as she was getting on the bus.

　　五、用作从属连词，引导“方式”副词从句。例如：

　　（8） You may act as you think fit.
　　（9） It is safer for you to do as you are told.

　　这些由"as"引导的从句可以节缩，如：

　　（10） It is safer for you to do as told.
　　（11） The meeting will be held as （it has been） scheduled.
　　（12） The weather here is not mild as （it is） in your country.

　　六、用作从属连词，引导“原因”副词从句。例如

　　（13） As the weather is fine, let's go fishing.
　　（14） We helped Tony, as he was a good man.

　　七、用作从属连词，引导“让步”副词从句。例如：

　　（15） Improbable as it seems, he is now Managing Director.
　　（16） Young as Sam is, he has performed his task creditably.

　　八、用作关系代词，引导形容词从句。例如：

　　（17） Is this the same thing as you showed me before?
　　（18） You can visit such places as you want to.

　　注意，“as”之前有“the same”或“such”和它挂钩。

　　九、协助组成短语与句型。例如：

　　（19） So as to: They departed early so as to reach the airport early.
　　（20） We have touched on the basic issues. As for thorny problems, let's look into them later.
　　（21） As long as you work hard, you will make it.
　　（22） I'll help you as best I can.
　　（23） Maria's idea is not so much a solution as a proposal to sound out our views on the project.