状语从句：
时间状语从句
引导词：when，while，as，after，before，since，until，as soon as，before，after.
When you think you know nothing, then you begin to know something.
地点状语从句
where，wherever引导。地点状语从句与定语从句的`区别，where引导定语从句时，从句前应有一个表示地点的名词作先行词；而状语从句前则无需先行词。
原因状语从句
Tom was late because he was badly ill yesterday.
引导词有because, as, since, for，seeing (that), now (that), considering (that)，in that
条件状语从句
引导词：if，unless，on condition that
If you want to know how old a woman is, ask her sister-in-law.
If引导的真实条件句，虚拟条件句条件状语从句中主句使用将来时态，而从句用一般现在时或现在完成时。