序数词：third.（表示第三）
基数词：three.（表示三个）
例句：
We waited three months before going back to see the specialist. 我们等了3个月才回去见那位专家。
Our team won three matches, drew one and lost two. 我们队胜了三局，和了一局，败了两局。
I studied in the same school with them for three years. 我和他们同过3年学。
Three characters are missing in this line. 这一行里脱了3个字。
He had three tries and failed each time. 他试了三回，每回都失败了。