第一节 主语从句 一、引导词 在复合句中充当主句主语的从句叫作主语从句。主语从句的常见引导词有： （一）从属连词：that, whether, if （二）连接代词：what, which, who, whose, whom, whatever, whichever, whoever, whomever （三）连接副词：how, when, where, why, however, whenever, wherever 二、that引导的主语从句 that引导主语从句时只起连接作用，没有实际意义，也不在从句中作任何成分。但that不能省略。 【例】That the earth moves around the sun is known to all. 地球绕着太阳转是众所周知的。 (从句作主语，谓语动词用单数形式。) 三、whether, if引导的主语从句 whether引导的主语从句既可以放在句首，也可以放在句末，但if引导的主语从句只能放在句末，前面需用it作形式主语。 【例】Whether you can succeed or not depends on how hard you work at it. 你能否成功取决于你努力的程度。(whether引导的主语从句放在句首) It is unknown whether/if he has agreed to my plan. 不知道他是否已经同意了我的计划。 (主语从句是whether/if he has agreed to my plan，it作形式主语) 四、连接代词或连接副词引导的主语从句 （一）连接代词what, who, which, whose, whatever, whoever, whichever等在从句中作主语、宾语、表语或定语。 【例】What he said just now is true. 他刚才所说的话是真的。(主语从句是What he said just now，what在从句中作said的宾语) Whoever breaks the law will be punished. 王子犯法与庶民同罪。(主语从句是Whoever breaks the law，whoever在从句中作主语) （二）what引导的主语从句一般按单数对待，但在实际使用中，其单复数取决于其成分的含义。 【例】What the kid wanted was only a new schoolbag. 那个孩子想要的只是一个新书包。(schoolbag是可数名词单数，谓语动词用单数) What they need are a car and some water. 他们需要的是一辆车和一些水。(a car and some water表示复数概念，谓语动词用复数) （三）连接副词when, where, why, how等在从句中作状语。 【例】Why they suddenly disappeared still remains a mystery. 它们为什么突然消失了还是个谜。 (主语从句是Why they suddenly disappeared，why句中作原因状语) When we’ll go for a picnic isn’t known. 我们什么时候去野餐还不知道。 (主语从句是When we’ll go for a picnic，when在从句中作时间状语） 五、it作形式主语 在通常情况下，that引导主语从句时，常用it作形式主语，而将that从句置于句尾。用it作形式主语通常有以下四种句型： （一）It+be+形容词+从句： It is necessary that... 有必要······ It is important that... 重要的是······ It is obvious that... 很明显······ （二）It+be+过去分词+从句： It is believed that... 人们相信······ It is known to all that... 众所周知······ It has been decided that... 已决定······ （三）It+be+名词（短语）+从句： It is common knowledge that... ······是常识 It is a surprise that... 令人惊奇的是······ It is a fact that... 事实是······ （四）It+不及物动词/动词短语+从句： It appears that... 似乎······ It happens that... 碰巧······ It occurs to sb. that... 某人突然想起······ It doesn’t matter whether... ······没有关系 六、whether和if的区别 连接词whether和if在用法上主要有以下两种区别： （一）whether可以引导所有名词性从句；if主要引导动词后的宾语从句和不在句首的主语从句，此时if和whether可以互换。 （二）wh ... ...
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