1、用在世界上独一无二的事物前。

如：Explore the surface of the moon.

2、用在序数词、形容词的最高级前。

如：This was the first step towards achieving a peace agreement.

3、用于上文已经提到过的人或事物。

如：He bought a new car.The car was very beautiful.

4、用在表示方位、乐器和影剧院的名词前。

如：The wind is blowing from the east.

5、用在江河、湖泊、海洋、山脉、群岛、沙漠和海湾等的名称前。

如：the Yellow River，the Pacific Ocean，the Alps.