定义及分类：在句中作状语的从句叫状语从句，也叫副词性从句。状语从句由从属连 词引导，可表示时间、地点、条件、原因、结果、目的、让步、比较、方式等。
状语从句连词一览表：
状语从句名称 连词
时间状语从句 when，as，while，since，before，after，till，until ,once，scarcely...when，hardly...when，no sooner...than,
as soon as = the moment = the minute = the second = the instant =immediately = directly = instantly，
by the time，every time，each time，
