名词性从句的用法讲解
引导名词性从句的连接词
1、 连接词：that,whether,if
2、 连接代词：what, whatever, who, whoever, whom, whose, which.
3、连接副词：when, where, how, why
名词性that-从句
1、由从属连词that引导的从句叫做名词性that-从句。
2、That-从句作主语通常用it作先行词，而将that-从句置于句末
名词性wh-从句
1、由wh-词引导的名词从句叫做名词性wh-从句。
2、Wh-从句作主语也常用先行词it做形式主语，而将wh-从句置于句末
if,whether引导的名词从句
1、yes-no型疑问从句
2、选择性疑问从句
否定转移
1、将think, believe, suppose, expect, fancy, imagine等动词后面宾语从句的否定词转移到主句中
2、将seem, appear 等后的从句的否定转移到前面。
3、有时将动名词，介词短语或整个从句的否定转变为对谓语动词的否定。
whether引导的从句常可以与连词or或or not直接连用，而if一般不能。如：
正： Let me know whether you can come or not.
误： Let me know if you can come or not.
2.当宾语从句提到句首时，只能用whether引导，而不能用if。
正： Whether it is true or not, I can’t tell.
误： If it is true or not, I can’t tell.
3. whether可以引导带to的不定式，if则不能。
正： I don’t know whether to accept or refuse.
误： I don’t know if to accept or refuse.
4. whether及其引导的成分可放于介词之后，作介词的宾语，但if不能。
如： 正： I worry about whether I hurt her feelings.
误： I worry about if I hurt her feelings.
5. whether可以引导从句，作主语、表语或同位语，而if不能。
如： 正： It was uncertain whether he would come.
误： It was uncertain if he would come.
正： His first question was whether Tom had arrived yet.
误： His first question was if Tom had arrived yet.
正： We must consider the question whether we will take these measures.
误： We must consider the question if we will take these measures.
