一、语法解析
名词性从句——表语从句
表语从句是在复合句中作表语的名词性从句，放在连系动词之后，一般结构是“主语＋连系动词＋表语从句”。可以接表语从句的连系动词有 be, look, remain, seem等。
1.连接词
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类别
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连接词
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例句
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从属连词
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that不作句子成分，也没有意义，通常不可省略
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My suggestion is that you should have patience. 我的建
议是你应该有耐心。
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whether 不作句子成分，但有“是否”的意义，一般不用if代替
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The question is whether we can cut down the costs of the product. 问题是我们能否降低产品成本。
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because, as if/through等
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He has to watch his weight.
That is because he has heart disease.他不得不注意自己的体重，那是因为他有心脏病。
It sounds as if someone is knocking at the door. 听起来
好像有人在敲门。
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连接代词
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who, whom, whose, what, which, whoever, whatever, whichever等。在从句中作主语、宾语、表语或定语
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The problem is who can complete the difficult task. 问题是谁能完成这项困难的任务。
This is just what we are always looking forward to. 这正是我们一直盼望着的。
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连接副词
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when, where, why, how等。在从句中作状语
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That is where he was born and brought up. 那就是他出生和被养大的地方。
Their difficulty is how they can clear their debts. 他们的困难是怎样才能还清债务。
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