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名词性从句 一、名词性从句的连接词 1．连接词that，whether和if (1)whether与if的用法比较 二者均可作“是否”讲，都可以引导名词性从句，引导宾语从句时可以互换。 I don't know whether/if he'll attend the meeting. 在下列情况下，常用whether，不用if。 ①whether引导从句可以放于句首。 Whether he comes or not makes no difference. ②whether可引导表语从句和同位语从句，if不可。 The question is whether it is worth trying. The question whether he should join the team has not been decided upon. ③whether可以作介词宾语，if则不可。 I haven't settled the problem of whether I'll lend him the money. ④whether后可以加不定式，if不可。 He didn't know whether to get married or to wait. ⑤可以用whether...or引导让步状语从句，意为“无论，不论”，if则不可。 Whether it rains or snows，I don't care. 2．连接代词 引导名词性从句的连接代词有：who，whom，whose，what，which，whatever，whichever，whoever。连接代词在句中既起连接作用，同时又充当主语、宾语、定语、表语等成分。 3．连接副词 引导名词性从句的连接副词有：when，where，how，why。连接副词在句中既是连接词，又作状语。 二、主语从句 1．主语从句在复合句中充当主语，大多数主语从句都可以用it作形式主语而把主语从句置于句尾。 2．that引导主语从句时可用it作形式主语，that不可省；what引导的主语从句表示“……的东西”时，一般不用it作形式主语；whatever，whoever，whichever一般也不用it作形式主语。 That she will succeed is certain. →It is certain that she will succeed. What he needs is more experience. | 
