序数词的用法作主语 e.g. The third of the month was a holiday.作表语 e. g. Who was the third?作定语 e.g. We live on the fifth floor.作宾语 e.g. I was among the first to learn of this.作同位语 e.g. Who is that man, the first in the front row?作状语 e.g. When did you first meet him?注：有时序数词并不指顺序，而是表示“再一，又一“的意思。此时序数词前要加不定冠词e.g. I want to make a second try.
