说序数词前要加the.如Septemberistheninthmonthoftheyear.那为什么有的序数词前就不加?如：Ashewasreadytoloadtheshipwithathirdtank,itsuddently.为什么这个是athirdtank,而例句是theninthmonth

Question

说序数词前要加the.如September is the ninth month of the year.
那为什么有的序数词前就不加?如：As he was ready to load the ship with a third tank,it suddently .为什么这个是a third tank,而例句是the ninth month

Answer 1

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....