一、理论常识
状语从句，属于副词性从句，简单说就是从句在句子中担任状语，分为时间、目的、地点、条件、方式、让步、比较、结果、原因9种状语从句。
时间引导词：when , after , before , while , until , till , since , as soon as , everytime , the moment等
地点引导词：where , wherever等
原因引导词：because , since=now that , as等
条件引导词：if , whether , unless , as long as ,on condition that , providing that等
结果引导词：so / such ... that , so等
目的引导词：in order that , so that等
让步引导词：though , although , however , whatever=no matter what even if , even though , as （倒装） 等
方式引导词：as , as if等
比较引导词:than , as ... as , the more ... , the more ... 等
