1、as引导原因状语从句
as引导原因状语从句，表示的是双方都知道的原因。可翻译成既然，由于。
如：As it was getting late, I decided to book into a hotel. 因为天色已晚，我决定找间饭店投宿。
2、as引导非限制性定语从句，代替整个主句，对其进行说明。As代替后面的主句，在从句中做主语。
如：As might be expected, the response to the question was very mixed. 正如所料，人们对于这个问题的观点不一。
扩展资料：
一、“as … as … 像…一样…”，这个结构是“as”最基本的用法之一。
eg:
1、You look as young as your daughter.
你看起来和你的女儿一样年轻。
2、I don’t think James is as nice as you think he is.
我不认为詹姆士像你想的那样善良。
二、“as”表达“作为，以…的身份;如同”的意思。
eg:
1、I used to work part-time as a barista.
我曾经兼职做过咖啡厅服务员。
2、Although Tony has a crush on Jess, she sees him as just a friend.
虽然托尼非常迷恋杰丝，但杰丝只把他当作朋友而已。
三、“as”可以用来说明事情的原因，译作“由于、因为”，它的语气要弱于表示直接因果关系的从属连词“because”。
eg:
1、Eating fruit and vegetables every day is essential, as they are healthy and nutritious.
每天吃水果蔬菜非常重要，因为这些食物既健康又有营养。
2、This is a fake pound coin, as the genuine one has different shape.
这枚一镑硬币是假的，因为真币的形状不同。
四、“as”作连词也有“随着…”或“在…的同时”的意思。
eg:
1、We all jumped as the monster appeared on the screen.
当那只怪物出现在荧屏上时，我们都被吓了一跳。
2、The baby started to giggle as she heard the music.
这个婴儿听到音乐后开始咯咯地笑了起来。
五、“as”作连词还有“尽管”的意思，其引导的从句需倒装，句子可以包含副词、形容词、名词等等。
eg:
1、Busy as he is, he always tries to spend time with his family.
虽然他很忙，但他总是想办法和家人在一起。
2、Famous as she is, she lives a very modest life.
尽管她很有名，但她仍然过得非常简朴、低调。
参考资料：百度百科-as