1. It is + 被強調部分 + that ...
該句型是強調句型。將被強調的部分放在前面，其它部分置於that之後。被強調部分可以是主語，賓語，表語或狀語。強調的主語如果是人，that可以由who換用。如果把這種句型結構劃掉後，應該是一個完整無缺的句子。這也是判斷強調句型與其它從句的方法。
It was about 600 years ago that the first clock with a face and an hour hand was made.
It was they that (who ) cleaned the classroom yesterday.
It was in the street that I met her father.
2. It is not until + 被強調部分 + that ...
該句型也是強調句型。主要用於強凋時間狀語，譯成漢語"直到...才..."，可以說是 not ... until ... 的強調形式。
It was not until she took off her dark glasses that I realized she was a famous film star.
= Not until she took off her dark glasses did I realize she was a famous film star.
= I didn’t realize she was a famous film star until she took off her dark glasses.
3. It is clear ( obvious, true, possible, certain....) that .....
該句型中it 是形式主語，真正的主語是that 引導的主語從句，常譯為"清楚(顯然，真的，肯定...)" 是主語從句最常見的一種結構。
It is very clear that he’s round and tall like a tree.
= That he’s round and tall like a tree is very clear.
4. It is important ( necessary, right, strange, natural...) that ...
該句型和上一個同屬一個句型。由於主句中的形容詞不同，that 後的從句中要用虛擬語氣(should + 動詞原形)，should 可以省去。建議記住該句型中的形容詞。
It is important that we (should) learn English well.
It is necessary that he (should) remember these words.
5. It is said (reported, learned....) that ...
該句型中的it 仍是形式主語，真正主語是that 引導的主語從句。該結構常譯為"據說(據報導，據悉...)"。
It is said that he has come to Beijing.
It is reported that another earth satellite has been put into orbit.
6. It is suggested ( ordered ... ) that ...
該句型和上一個同屬一個句型。主句中的過去分詞是表示請求，建議，命令等詞時，that 後的從句要用虛擬語氣(should + 動詞原形)，should 可以省。常譯為"據建議;有命令...)
It is suggested that the meeting ( should ) be put off.
It was ordered that we ( should ) arrive there in two hours.
7. It is a pity ( a shame ... ) that ...
該句型中，that後的從句一般用虛擬語氣(should + 動詞原形)，should可省去.表示出乎意料，常譯為"竟然"。沒有這種意義時，則不用虛擬語氣。
It is a pity that such a thing ( should ) happen in your class.
這種事竟然發生在你們班上，真是遺憾!
It is a pity that he is ill. 他生病了，真遺憾!
8. It is time ( about time ,high time ) that ...
該句型中that 後的從句應該用虛擬語氣，值得注意的是① 常用過去時態表示虛擬.② 有時也用should + 動詞原形，should 不能省。常譯為"是(正是)...的時侯..."。
It is time that children should go to bed.
= It is time that children went to bed.
9. It is the first ( second ... ) time that ...
該句型要和上一個句型區別開來。該句型中的 that 從句不用虛擬語氣，而用完成時態。至於用什麼完成時態，由主句的謂語動詞的時態決定。如果是一般現在時，後面從句用現在完成時態;如果是一般過去時，後面從句則用過去完成時態。該結構中 that 可以省去;it有時用 this 替換.常譯為"是第一(二)...次..."。
It is the first time I have been here.
= This is the first time I have been here.
10. It is .... since ...
該句型主要用作處理瞬間動詞的完成時，又要和表示一段時間的時間狀語連用的問題。主句中是時間作表語，其時態是現在時或完成時，since 引導的從句通常是一般過去時態，而且是瞬間動詞。如果主句是一般過去時，從句則用過去完成時。
It is ( has been ) 5 years since his father died.
11. It is ... when ...
該句型中的 when 引導的是一個時間狀語從句，主句中的 it 指時間，表語由具體的時間充當。常譯為"當...的時候，是..."。
It was 5 o』clock when he came here.
12. It be ... before ...
該句型主句中的 it 指時間, 主句中的時態常是將來一般時或過去時兩種時態.主句中的表語多是long, not long , 3 days , 2 weeks 等表示時間段的詞或短語。常譯為"...之後..."。
It was 3 days before he went to Beijing.
It will be not long before he finishes his job.
13. It happens (seems, looks, appears ) that...
該句型中it是形式主語，that 引導的是主語從句，主句中的happen , seem等詞是不及物動詞.
It happened ( so happened ) that he met his teacher in the street. 碰巧..
It seems that he will be back in a few days. 看來...
14. It takes sb. ... to do sth.
該句型中的不定式是真正的主語，it是形式主語，句型中的直接賓語是時間。常譯為"做...要花費某人..."。
It took thousands of people many years to build the Great Wall.
15. It is no good (use ) doing sth.
該句型中的真正主語是動名詞短語，主句中的表語可以是no good , ( not any good ) , no use , ( not any use )。
It is no good learning English without speaking English.
16. It doesn’t matter whether ( if ) ...
該句型中whether(if) 引導的從句是真正主語，該句型常譯為 "不論(是否)...沒關係...。
It doesn’t matter if they are old.
17. It is kind ( of sb. ) to do sth.
該句型中的不定式短語是真正主語，如果不定式的邏輯主語是由 of引起，主句中的形容詞必須是能表示邏輯主語特徵的形容詞。常見的有： bad , brave , careless, clever , cruel , foolish , good (好心的), honest , horrible , kind , lazy , modest , naughty , nice(有教養的), polite, rude , silly , stupid , wise , wrong(錯誤的)等。 這個句型可以改寫為：sb. is kind to do sth.
It is kind of you to say so.
= You are kind to say so.
18. It is necessary ( for sb. ) to do sth.
該句型與上一個同屬一個句型。如果不定式的邏輯主語是由for引起，主句中的形容詞通常是表示重要性，緊迫性，頻繁程度，難易，安全等情況的形容詞。常見的形容詞有：① important, necessary, natural ② easy , safe , common , normal , hard , difficult , dangerous , unusual, rare , impossible , pleasant等。
在①中的形容詞作表語可以用從句改寫， 如：
It is important for her to come to the party.
= It is important that she (should ) come to the party
19. It looks ( seems ) as if ...
該句型中it無意義。 as if 引導一個狀語從句。常譯為，"看起來好象..."如果與事實不相符合，則用虛擬語氣.
It looks as if he is ill.(真的病了)
It looks as if he were ill. (沒有生病)
It seemed as if he were dying.
20. We think it important to learn a foreign language.
該句型中的it 作形式賓語。為了記憶方便我們可稱該句型為"6123結構"。
6指主句中常用的動詞：think, believe, make, find, consider, feel;
1指的是形式賓語it;
2指的是賓補的兩種形式：形容詞或名詞;
3指的是真正賓語的三種形式：不定式短語，動名詞短語或that引導的賓語從句。
We think it our duty to clean our classroom every day.
He felt it important learning English well.
They found it difficult that they would finish their work in two days.