学习表语从句五大要素
学习表语从句五大要素
表语从句位于连系动词之后，引导表语从句的词有that, what, how, when,where, why, because, as if 等。 要掌握好表语从句，我们在学习中必须要注意下面这些要点：
一、表语从句要用陈述语序。如
This is where the famous scientist was born.
This is why she is so happy today.
二、that 和what 在引导表语从句时， 作用和意义都不一样。That 本身没有词义，在句中仅起连接作用，而不充当句子成分；what 则表示“所... 的（人或事）”，在表语从句中充当主语或宾语等。如： The fact is that more than seventy percent of the earth ’s surface is covered by water.(that 不作句子成分)
What he told you was what had been discussed at the meeting.(第一个what 作主句中的宾语；第二个what 在表语从句中主语) 。
三、if 与whether 均意为“是否”， 但引导表语从句时，只能用whether, 不用if
The question is whether we can finish our work by tomorrow evening.
四、当主句的主语为reason ， 或者是由Why 引导的从句时，与它们相关的表语从句的连接词多用that. 如：
Why she failed in physics exam was that she was too careless.
五、as if, as through 引导表语从句时，从句谓语常用虚拟语气。这是
因为从句中的情况与事实不符。具体来说，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，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。如：
Lilei is now in a new jacket. He looks as if he were an American boy. The girl is giving us a vivid description of the moon. It seems as if she had been to the moon many times.
It looks as if it might rain
但是，如果as if ,through 引导的表语从句所表示的情况与事实相符，从句则用陈述语气。如：
The cloud are gathering. It looks as if it is going to rain.