1、二.主语从句引导词及其用法特点连词that，不能省略，用于陈述句，在句子中不作成分；连词whether，if不用于句首，用于一般疑问句，在句子中不作成分；连接副词when，where，why，how，用于特殊疑问句，在从句中作状语；连接代词who，whom，what，用于特殊疑问句，在从句中作主语，宾语或表语；which，whose，用于特殊疑问句，在从句中作定语，后面接连词使用
2、三.it形式主语句型猾诮沓靥(一)It is+形容词＋that主语从句It is clear/obvious that...It is possible/likely that...It is natual that...It is certain that...（二）It is+过去分词+that主语从句It is said that...It is reported that...It is generally believed that...It has been found that...It should be noted that...（三）It＋不及物动词＋that主语从句It appears/seems that...It follows that...It happens that...It turns out that...It comes about that...（四）It is＋名词短语＋that主语从句It is a pity that...It is a fact that...It is an honor that...It is a shame that...It is my belief that...It is a good news that...It is common knowledge that...（五）其他结构It dawns upon/on sb.that...It occurs to sb.that...It doesn't need to be bothered that...It makes no difference that...It is of litter consequence that...
