2.構成：關聯詞+簡單句

3.引導主語從句的關聯詞有三類：

（1）從屬連詞that.

如：That they were in truth sisters was clear from the facial resemblance between them.

很明顯，她們確是親姐妹，她們的臉型很相似。

（2）從屬連詞whether.如：

Whether he'll come here isn't clear. 他是否會來這里還不清楚。

（3）連接代詞who，whom，whose，what，which，whoever，whatever，whichever

連接副詞where，when，how，why.如：

What she did is not yet known. 她干了什么尚不清楚。

How this happened is not clear to anyone. 這事怎樣發生的，誰也不清楚。

Whoever comes is welcome. 不論誰來都歡迎。

Wherever you are is my home - my only home. 你所在的任何地方就是我的家——我唯一的家。

難點釋疑：

1.主語從句能用it作形式上的主語。常以it作形式主語的句型有：

A. It+be+形容詞（obvious，true，natural，surprising，good，wonderful，funny，possible，likely，certain，probable，etc.）+that從句。如：

It is certain that she will do well in her exam. 毫無疑問她考試成績會很好。

It is probable that he told her everything. 很可能他把一切都告訴她了。

B. It+be+名詞詞組（no wonder，an honour，a good thing，a pity，no surprise，etc.）+that從句。如：

It's a pity that we can't go. 很遺憾我們不能去。

It's no surprise that our team should have won the game. 我們沒贏這場比賽真意外。

C. It+be+過去分詞（said，reported，thought，expected，decided，announced，arranged，etc.）+that從句。如：

It is said that Mr. Green has arrived in Beijing. 據說格林先生已經到了北京。

It is reported that China has sent another man-made earth satellite into orbit. 據報道中國又成功地發射了一顆人造地球衛星。

D. It+seem，happen等不及物動詞及短語+that從句。如：

It seems that Alice is not coming to the party at all. Alice似乎不來參加晚會。

It happened that I was out that day. 碰巧我那天外出了。

E. 當主語從句出現在感嘆句中時，要以it作形式主語，而把主語從句后置。如：

How strange it is that the children are so quiet! 孩子們這么安靜真奇怪！

2.注意連接代詞whoever，whatever，whichever等引導主語從句的含義：

Whoever comes will be welcome. (whoever=the person who)來的人將受到歡迎。

Whatever he did was right. (whatever=the thing that)他所做的事情是正確的。

Whichever of you comes in will receive a prize. (whichever=anyone of you who)你們當中不論哪個進來將會得到獎勵。