用作状语的句子叫状语从句。
一、状语从句可分为时间、地点、原因、目的、结果、让步、比较、方式和条件等状语从句。
I will call you when I get home.
我到家后就打电话给你。（时间状语从句）
she cried because she was upset.
她哭了，因为她心情不好。（原因状语从句）
Although he was exhausted, he stayed up to finish his homework.
虽然他筋疲力尽，但是他还是熬夜完成作业。（让步状语从句）
She is so busy that she can’t call you.
她太忙了，以致无法打电话给你。（结果状语从句）
二、通过状语从句的引导词可以判定是哪类状语从句
时间状语从句的引导词通常有：
when, whenever, as, while, as soon as, before, after, since , till, until，by the time, every time, the minute, the moment, the instant, immediately , directly, no sooner … than, hardly …when, hardly…before
地点状语从句的引导词通常有：
Where, wherever
原因状语从句的引导词通常有：
because, since, as, for, seeing that
目的状语从句的引导词通常有：
so that, in order that, lest, in case
结果状语从句的引导词通常有：
so … that, so that, such … that, such that
让步状语从句的引导词通常有：
though, although, even if, even though, while;
no matter what/who/where/when/how/which;
whatever, whoever, wherever, whenever, however, whichever;
