一、That可以做副詞，代詞，形容詞和連詞，但是做連詞時是最常見的，也是最難鑒別的，that 用作連詞，引導名詞性從句,狀語從句和強調句。
1. that在名詞性從句中。
①引導賓語從句。及物動詞后的引導詞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。通常采用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;而后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、盡管"。
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.
3. 引導強調句。
It is Mrs. White that makes the decision in her family, not her meek little husband.
It is an ill wind that blows nobody good.
附加：that引導定語從句(做關系代詞)
Is he the man that wants to see you?
The package that you are carrying is about to come unwrapped.
二、While可以做名詞和連詞，做連詞時又可分為從屬連詞和并列連詞。
做從屬連詞可以引導時間狀語從句，讓步狀語從句，條件狀語從句。
(1)引導時間狀語
Wemuststrikewhiletheironishot.趁熱打鐵。
(2)引起讓步狀語從句，意思是"雖然...但是...."、"盡管...但是..."(多放于句首)
Whileheloveshisstudents，heisverystrictwiththem..
雖然他愛他的學生，可是他對他們很嚴格。
(3)引起條件狀語，意思是"只要"
Whilethereislifethereishope.
只要生命存在，就有希望。
While作并列連詞用，意思為"而，然而"，表對比。而but表轉折。
Honeyissweet，butthebeestings.
蜂蜜很甜，但蜜蜂有刺蜇人。
三、which可以做疑問代詞和關系代詞。
1. 用作疑問代詞時，意思是"哪一個,哪一些"
Which is my seat? 哪個座位是我的?
2. 用做關系代詞時，意思是"那一個,那一些"
He also had a gun with which to defend himself. 他還有一把自衛用的槍。
四、where可以做副詞，連詞，和代詞。
當副詞時，可分為疑問代詞和關系代詞：
1. (用作疑問副詞)在哪里往哪里從哪里在哪一點上
The driver asked me where I wanted to go.
司機問我想去哪里。
Where shall we go?
我們去哪里?
2. (用作關系副詞,引導關系從句)在那里往那里
That’s where we differ.
那是我們的分歧所在。
This is the city where I was born.
這是我出生的城市。
當連詞引導地點狀語從句，意思是"在...處到...的地方...的地方"
I’ll meet him where I first met you.
我將在初次見你的地方與他會面。
當代詞，意思是"哪里,何處"
Where does he come from?
他是哪里人?
