一、主语从句全部引导词，分两大类第一类：不充当句子成分（只起连接作用）that / whether1. that无含义，从句主谓宾完整时使用。2. whether含义：是否，不能省略，不可用if引导主语从句。例：Whether she will come remains unknown.第二类：必须在从句中充当成分（主语、宾语、定语）1. 指事物• what = the thing that（主/宾）• which 哪一个（有选择范围，做主/宾）2. 指人• who 谁（作主语）• whom 谁（作宾语，口语也可用who）• whose 谁的（作定语）3. 作状语（副词类，不作主宾）• why 原因• when 时间• where 地点• how 方式、怎样口诀：句子完整：that / whether缺主宾：what, who, whom, which, whose缺状语：when, where, why, how二、每种引导词例句（主语从句）1）who（人，主语）Who will take charge hasn't been decided.谁来负责还没定。2）whom（人，宾语）Whom we choose matters little.我们选谁无关紧要。3）whose（定语）Whose plan is better is clear.谁的方案更好一目了然。4）which（有范围，哪一个）Which one we pick makes no difference.5）when（时间状语，句子完整）When we start is still up in the air.