1.表示上文已经提到的人或物,或特指某人或某物.
例如：I'm very interested in the film.
Give me the book.
Who is the girl you just said hello to?
2.表示世界上独一无二的东西.
例如：the air ,the earth ,the moon,the sun,the sky
3.对两个人或物比较时起特定作用的比较级之前.
例如：He is the taller of the two children in his family.
4.用在形容词最高级、序数词和last,next,only,same,right,wrong之前
例如：the largest room,the second story,the same school,the only one,the wrong way