判断as 引导的是“时间”还是“原因”从句，告诉网友一个窍门：

1. 当as 从句的谓语动词表示状态时，一般是“原因从句”。

He had to walk upstairs as the lift was out of order.

was out of order：是“系表结构”表状态。所以是“原因从句”。又如：

As he is a troublemaker, no one likes to work together with him. 因为他这个人爱惹是生非，谁都不愿同他共事。

2. as 表示时间时，主、从句中的两个动作一都是延续性的，而且都是同时进行的，意为“一边...一边...；随着...”。例如：

But as time passed, I grew bored with an idle lifestyle. 

不过，随着时光消逝，我渐渐厌倦了清闲的生活方式。

She sang as she walked.

她边走边唱歌。