as当连词的含义差别

as作为连词，常见的有以下4种情况
（1） 译为“像……一样”，引导方式状语从句，如
You must do as I tell you to. 你必须按我告诉你的去做。

（2） 译为“随着” 引导时间状语从句，如
As time goes by, everything will change.
As he grew older, he lost interest in everything except gardening.
随着他慢慢长大，他失去了对除了园艺以外的其他所有事情的兴趣。

（3）译为“因为” 引导原因状语从句，如
As you were not there, I left a message. 你不在哪里，我留了个纸条。

（4）译为“尽管，即使” 引导让步状语从句
Child as he is, he knows a lot. 虽然是个小孩，他知道很多。
Poor as he is ,he is generous. 虽然很穷，他很慷慨。

另外，虽然你没问，我还是一起说了吧。
as 还可以做介词，翻译为“作为”，如
as a school boy
treat it as a joke

也可以做副词，翻译为“同样的，一样的”
as easy as ABC
as soon as (it is) possible
as busy as bees