一个英语问题 急 谢谢

序数词前一般要加the,如上句子。
如果用a,这是因为:相同的一个动作的重复。
to load the ship with the 1st tank
to load the ship with a 2nd tank ...
老式的英语课本第五册“渔夫与魔鬼”的故事里有这一段描写，就是关于这个问题的：
One moring,the fisherman went out early to the sea.He cast his net for the first time,and drew in the body of an animal.He cast it "a second time",and drew in an old basket full of sand.He cast it "a third time",and drew in a lot of stones. ...

第九个月是固定的用the 而那句子里的a third tank是特指那个tank所以用a
a 和 the 都是定冠词 本质上是一样的

楼上的，a和the 怎么可能都是定冠词？