1．特指某(些)人或某(些)物或双方都知道的人或物。
The young man is the student who I taught 10 years ago.这个年轻人是我十年前教过的学生。
Open the door, please！请把门打开！
2．指上文提到过的人或事物。
There was a chair by the window.On the chair sat a young woman with a baby in her arms.
窗户附近有一把椅子。椅子上坐着一位怀里抱着一个婴儿的年轻妇女。
3．指世上独一无二的事物。
Which is the biggest, the sun, the earth or the moon? 太阳、地球和月亮哪一个最大？
[名师点津]
如果名词前有修饰语， 可用不定冠词：
a bright moon 一轮明月
4．和单数名词连用表示一类人或事物； 与形容词或分词连用， 表示一类人。
The train goes faster than the bus.
火车比公共汽车快。
They buried the dead and took the wounded to the hospital at once.
他们掩埋了死者， 把受伤的人立刻送进了医院。
5．用在序数词和形容词最高级及形容词only, very, same等前面。
—Where do you live？你住在哪？
—I live on the second floor.我住在二层。
He was the only person in his office who was invited to the party.
他是办公室里唯一一个被邀请参加聚会的人。
