3、表语从句

　　表语：说明主语的性质、特征、状态或身份，说明主语是什么或者怎么样。总之表语是对主语的解释和说明，是主语具体化，并且常与连系动词一起使用。

　　表语从句：在复合句中作表语的从句, 就叫做表语从句。表语从句一般放在系动词之后,结构是“主语+系动词+表语从句”。

　　★连系动词：be动词、表示持续的系动词(keep, remain, stay)、感官动词feel(摸起来，感觉) , smell(闻起来) , sound(听起来) , taste(尝起来，吃起来) 等、表示变化的系动词(become, grow, turn, fall, get, go,)、表终止的系动词prove, turn out(结果是，证明是)、seem, appear(看起来……)

　　连系动词通常不用于被动语态和进行时态中。

　　He has become what he wanted to be ten years ago.

　　他已经成为了他10年前想成为的样子。

　　His suggestion is that we should stay calm.

　　他的建议是，我们应该保持冷静。

　　1.表语从句的引导词

　　①从属连词

　　that / whether /as if /as though/as/because

　　(1) that引导表语从句本身没有词义，在句中只起连接作用，不充当句子成分，一般不能省略。

　　That fact is that more than seventy percent of the earth’s surface is covered by water.

　　连接词that一般不能省略，但当主句中含动词do的某种形式时，that可以省略。

　　What I want to do is (that) I can go up to him and thank him. 我想做的事是走到身边去感谢他。

　　(2) whether引导表语从句表示“是否”,但不充当句子的成分。

　　The question is whether we can finish our work by tomorrow evening.

　　if 与whether均意为“是否”，但引导表语从句时，只能用whether, 不能用if。

　　(3)as if/though“好像”，引导表语从句时要注意语态。

　　如果句中的情况与事实不相符，从句多用虚拟语气。如果从句表示与现在事实相反,谓语动词用一般过去式;如果从句表示与过去事实相反时,谓语动词要用“had + 过去分词 ”，如果从句表示将来的可能性不大，用would (might ,could )+动词原形。

　　Li Lei is now in a new jacket. He looks as if he were an American boy. (现在事实相反)

　　The girl is giving us a vivid description of the moon. It seems as if she had been to the moon many times. (与过去事实相反)

　　It looks as if it might rain. (与将来事实相反)

　　但是，如果as if/though引导的表语从句所表示的与事实相符，从句则用陈述语气。

　　The clouds are gathering. It looks as if is going to rain.

　　(4) as引导表语从句

　　He looked just as he had looked ten years before.

　　他看起来还与十年前一样。

　　(5) because引导表语从句

　　常用结构：This/That/It is/was because...

　　That is because I don’t like Chinese.