表语从句讲解及专项练习
概念：表语从句是在复合句中作表语的名词性从句。
放在系动词之后,一般结构是“主语+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。
★ The trouble is that we are short of money.困难是我们资金短缺。
★ That is why stone walls are used instead of fences around New England fields.这就是为什么在新英格兰用石头墙而不用栅栏的原因。
★ At that time, it seemed as if I couldn't think of the right word anyhow.当时,我似乎怎么也想不出一个恰当的字眼来。
引导表语从句的词：
从属连词that、whether、as though、as if（That引导表语从句时，在口语中，间或可以省略。）
关系代词who, what, which, whom, whose, whatever, whoever, whomever, whichever等；
关系副词when, where, why, how, however, whenever, wherever等。
※由从属连词that，whether引导的表语从句。
that在引导表语从句时无词义，而whether有词义，意为、“是否”。这时主句的主语常常是些抽象名词，如question(问题)，trouble(麻烦)，problem(问题)，result(结果)，chance(可能性)，suggestion(建议)，idea(想法)，reason(理由)等。表语从句对主句主语进行说明、解释，使主语的内容具体化。
例如：
★ The trouble is (that) she has lost his money. 麻烦的事是他丢了钱。
★The question is whether we need more ice cream.问题是我们是否还需要一些冰淇淋。
★The problem was that it was too valuable for everyday use.问题是它作为日常之用太贵重了。
★What she couldn’t understand w as that fewer and fewer students showed interest in her lessons. 我们不能理解越来越少的学生对他的课不感兴趣。
※由关系代词引导的表语从句。
关系代词who, what, which, whom, whose, whatever, whoever, whomever, whichever等引导表语从句，在句中作主语、宾语、表语，关系代词不能省略。
例如：
★The question is which of us should go.问题是我们哪一个应该去。
★The problem was who could do the work.问题是谁能做这项工作。
★That's what he is worrying about.那就是他在担心的事。
★That's what we should do.那是我们应该做的。
※由关系副词引导的表语从句。
关系副词when, where, how, why 除在句子起连接作用外，在从句中还充当时间，地点，方式或原因状语，本身具有词义。
例如：
★Go and get your coat. It's where you left it. 去把雨衣拿来。就在你原来放的地方。
★I had neither a raincoat nor an umbrella. That’s why I got wet through. 我们既没伞也没雨衣，这是我们淋湿的原因。
★That is how mice ruin many stores of grain every year.那就是老鼠是怎样每年损害大量粮食的。
★That is what he is worried about.那就是他所担心的。
※由连词because，as if/as though等引导的表语从句。
★It looked as if it was going to snow.看起来好像要下雪了。
★That's because we never thought of it.这是因为我们从未想过此事。
★It seems as if he didn’t know the answer.好像他不知道答案。
注意
A. 表语从句一定要用陈述语序。
False: The question is when can he arrive at the hotel.
Right: The question is when he can arrive at the hotel.
B. 不可以用if，而用whether 连接表语从句(as if 例外）。
引导宾语从句时可以互换if/whether 位于介词后要用whether
位于句首时要用whether。
引导表语从句，主语从句，同位语从句时要用whether。
False: The question is if the enemy is marching towards us.
Right: The question is whether the enemy is marching towards us.
Right: It looked as if he had understood this question.
C.不像宾语从句，在有表语从句的复合句中，主句时态和从句时态可以不一致。
Right: The question is who will travel with me to Beijing tomorrow.
Right: The question is why he cried yesterday.
D. that在表语从句中不可以省掉。
基本用法
表语从句只能置于主句之后，而主句的动词只能是联系动词。
名词性从句在be等系动词后作表语时被称为表语从句
例如：
★The problem is how we can get the things we need.
问题是我们怎样能弄到我们需要的东西。(how 在表语从句中充当方式状语)
★The scissors are not what I need. 这把剪刀不是我所需要的。(what 在表语从句中充当宾语)
★What I told him was that I would find him a good play. 我告诉他的是我会给他找个好剧本。(what在主语从句中作直接宾语，that作为表语从句的引导词在该表语从句中不充当句子成分，不能省略)
