We use ordinal numbers to see which comes first.

当我们看是哪个先的时候，使用序数。

And fiftieth is the correct way to write the ordinal number.

而 fiftith 才是序数词的正确写法。

Finally, you might also hear ordinal numbers used as an adjective.

最后，你可能还会听到序数用作形容词。

Ordinal numbers are numbers that show the order of things.

序数词表示的是事物的顺序。

Ordinal numbers are one important area of grammar that connects with the Olympics.

序数是与奥运会相关的一个重要语法领域。

All of the other ordinal numbers end in a TH.

所有其他以TH结尾的序数词。

It's very rare to see an unabbreviated ordinal number in a written date.

我们非常常用这种写法当我们在写整个日期的时候。

But in the Olympic games, ordinal numbers are of central importance.

但是在奥运会上，序数才是最重要的。

When you're ordering things, so when ordinal numbers like second, fifth, are used as adjectives.

当你在给某些事物排序时，那么这时序数词像是第二，第五，作为冠词使用。

Ordinal numbers can act as nouns, adjectives, or adverbs.

序数可以充当名词、形容词或副词。