状语从句在句中作状语，按功能分为时间、条件、原因、结果、目的、让步、比较等从句。
要点讲解
- 时间状语从句：when, while, as, before, after, until, as soon as（主将从现）：I'll call you as soon as I arrive. 我一到就给你打电话。
- 条件状语从句：if, unless（=if...not）：If it rains tomorrow, we'll stay at home. 如果明天下雨，我们就待在家。
- 原因状语从句：because, since, as：He didn't come because he was ill. 他没来，因为他病了。
- 结果状语从句：so...that...（如此……以至于……）：He is so young that he can't go to school. 他太小，不能上学。
- so that 目的状语从句（以便）：Get up early so that you can catch the bus. 早起以便赶上公交车。
- 让步状语从句：although/though（虽然）：Although he is old, he works hard. 虽然他老了，但他工作努力。
- 比较状语从句：than（比），as...as（和……一样）：He is taller than I（am）. 他比我高。
- until/till 直到：I waited until he came back. 我一直等到他回来。
- so...that 与 such...that：so + 形/副，such + 名词：He is so good a boy that we all like him. = He is such a good boy that we all like him.
- as soon as/if/when/unless 引导的从句，主句将来时从句用现在时（主将从现）。
经典例句
- Unless you work hard, you will fall behind.
除非你努力学习，否则你会落后。 - The box is so heavy that I can't carry it.
这个箱子太重了，我搬不动。 - We were watching TV while mother was cooking.
妈妈做饭时我们在看电视。
易错提醒
- because 不与 so 连用，although 不与 but 连用；主将从现：if/when/as soon as 从句用一般现在时表将来。