①用于大家心目中都知道的人或事物。如：
Could you please help me to carry the box upstairs？你能帮我把这盒子搬到楼上吗？
Who is on duty today？ Clean the blackboard，please.今天谁值日？请擦一下黑板。
②用于指上文所提到的事物。如：
I have a son and a daughter.The son is a worker，and the daughter is a nurse.我有一个儿子、一个女儿。儿子是工人，女儿是护士。
There is an apple on the table.The apple looks very nice.桌子上有个苹果。苹果看起来很不错。
③用于带有后置定语的名词前，此处的后置定语可以是分词、介词短语或定语从句。如：
Do you know the woman standing near the window？你认识站在窗户旁的那个女人吗？
The cat under the tree is black.树下那只猫是黑色的。
④用于具体的情景之中。如：
I study in No.1 Middle School.The teachers are very patient and the students are very friendly and helpful.The classrooms are very big and bright.我在一中就读。那里的老师很有耐心，学生很友好，而且乐于助人。教室宽敞明亮。
⑤用于独一无二的名词前。如：
The earth goes round the sun，and the moon goes round the earth.地球围绕太阳转，月亮围绕地球转。
The bird is flying high in the sky.小鸟在天空高高飞翔。
Lu Xun is one of the greatest writers in the world.鲁迅是世界闻名的作家之一。
⑥与单数名词连用表示一类人或事物。如：
The book is different from the magazine.书不同于杂志。
The elephant is a very big animal.大象是非常庞大的动物。
⑦与某些形容词连用，表示一类人或事物，当主语用时通常作复数用；和名词连用，表示全体。如：
The old should bring up the young，and the young should provide for the old.老年人应该抚养年幼者，年轻人应该赡养老人。
The beautiful always gives us pleasure.漂亮的东西总是给人们以享受。
The music is loud enough to wake up the dead.音乐声音太大了，死人也会被吵醒的。
⑧用于山川、湖泊、海洋、群岛、建筑等专有名词前；也用于乐器名称之前。如：
The Yangtze River is the third longest river in the world.长江是世界上第三长的河流。
A man who hasn't been to the Great Wall is not a true man.不到长城非好汉。
⑨定冠词常相当于指示代词的含义。如：
Whose is the book？这书是谁的？
The poor little boy has to spend four or five hours doing his homework every day.那个可怜的小男孩每天要花四五个小时做作业。
⑩定冠词常相当于every，each，per，a的含义。如：
The cleaner is paid by the hour.清洁工是以小时计工资的。
⑪在一些用法中相当于形容词性的物主代词，但绝不能再用形容词性的物主代词。如：
The teacher patted him on the shoulder and said，“Study hard.”老师拍拍他的肩膀说：“好好学习。”
The woman hit me in the face and I struck her on the back.那女人打了我的脸，我打了她的背。
⑫用在序数词或形容词副词最高级前。如：
She was the second student to come to the classroom this morning.今天早上她是第二个到教室的学生。
Who runs the fastest in your class？你们班谁跑得最快？
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