It做形式主語，代替由不定式，動名詞短語或是從句所表示的真正的主語。如It’s no use talking to him about it.
It做形式賓語，代替一個由不定式，動名詞，或是賓語從句，如I think it no use arguing with him.
it可以指季節,時間, 距離
如 It was mid summer.
It’s only five miles.
同時在強調句中，It + be + 要強調的部分+ that(who, whom) + 句子其他部分 .這個句型很重要，記住即可。
that有些固定的搭配 如 so that ，such that。
that 用作連詞，引導名詞性從句,狀語從句和強調句。
1. that名詞性從句。
①引導賓語從句。及物動詞後的引導詞that可省略。
I didn't expect (that) he could win the championship.
The teacher pointed out that Tom was not working hard enough.
② 引導主語從句。通常採用it作形式主語的句型。
That the earth goes around the sun is known to everyone.
（It is known to everyone that the earth goes around the sun.）
③引導表語從句。
The trouble is that we are short of money.
④引導同位語從句。
引導同位語從句的that和引導定語從句的that是不同的。前者只起語法作用，在從句中不作任何成分；而後者在定語從句中作主語、賓語或表語。舉例說明：
The news that he resigned from office surprised us.
The idea that he holds is very common nowadays on campus.
2. that引導狀語從句
①引導目的狀語從句。
Bring it nearer that I may see it better.
②引導結果狀語從句。
What have I done that he should be so angry with me?
③引導原因狀語從句。
I am afraid that I will fail in the driving test.
④引導讓步狀語從句。意為“雖然、儘管”。
Difficult that/as the task was, they managed to accomplish it on time.
⑤引導條件狀語從句。意為“假使、假設”。
Supposing that you were in my position, what would you do?
On condition that you were lost in the desert, you should ask for help as soon as possible.
It做形式主語，代替由不定式，動名詞短語或是從句所表示的真正的主語。如It’s no use talking to him about it.
It做形式賓語，代替一個由不定式，動名詞，或是賓語從句，如I think it no use arguing with him.
it可以指季節,時間, 距離
如 It was mid summer.
It’s only five miles.
同時在強調句中，It + be + 要強調的部分+ that(who, whom) + 句子其他部分 .這個句型很重要，記住即可。
that有些固定的搭配 如 so that ，such that。
that 用作連詞，引導名詞性從句,狀語從句和強調句。
1. that名詞性從句。
①引導賓語從句。及物動詞後的引導詞that可省略。
I didn't expect (that) he could win the championship.
The teacher pointed out that Tom was not working hard enough.
② 引導主語從句。通常採用it作形式主語的句型。
That the earth goes around the sun is known to everyone.
（It is known to everyone that the earth goes around the sun.）
③引導表語從句。
The trouble is that we are short of money.
④引導同位語從句。
引導同位語從句的that和引導定語從句的that是不同的。前者只起語法作用，在從句中不作任何成分；而後者在定語從句中作主語、賓語或表語。舉例說明：
The news that he resigned from office surprised us.
The idea that he holds is very common nowadays on campus.
2. that引導狀語從句
①引導目的狀語從句。
Bring it nearer that I may see it better.
②引導結果狀語從句。
What have I done that he should be so angry with me?
③引導原因狀語從句。
I am afraid that I will fail in the driving test.
④引導讓步狀語從句。意為“雖然、儘管”。
Difficult that/as the task was, they managed to accomplish it on time.
⑤引導條件狀語從句。意為“假使、假設”。
Supposing that you were in my position, what would you do?
On condition that you were lost in the desert, you should ask for help as soon as possible.