"as" 作为引导词时,可以引导多种类型的从句,具体如下:

原因状语从句:

表示原因或理由,相当于"because"。例如:

As it was getting late, we decided to go home.

时间状语从句:

表示时间或时间关系,相当于"when"或"while"。例如:

As I was reading the newspaper, the bell rang.

方式状语从句:

表示方式或方法,相当于"in the way that"或"just as"。例如:

She sings as beautifully as her sister.

比较状语从句:

用于比较,相当于"like"或"as"。例如:

He works as hard as his brother.

让步状语从句:

表示让步关系,相当于"although"或"though",但更常用于非正式或口语中。例如:

As it was raining, we stayed at home.

定语从句:

用于修饰名词,可以引导限定性定语从句和非限定性定语从句。例如:

The book which is on the table is mine.

Such people as he are rare.

需要注意的是,"as" 作为介词时,通常不引导从句,而是后面直接跟名词。例如:

She works as a teacher.

综上所述,"as" 作为引导词时,可以引导原因状语从句、时间状语从句、方式状语从句、比较状语从句和让步状语从句,具体用法取决于其在句子中的功能和上下文。