一，记住基数词
序数词来源于基数词。开始学习英语的时候，总是有几个基数词写错。one two three four five six seven eight nine ten zero eleven twelve thirteen fourteen fifteen sixteen seventeen eighteen nineteen twenty twenty-one twenty-two twenty-three thirty thirty-five forty forty-one fifty-three sixty-one seventy-five eighty-two ninety-nine one hundred
上面这些基数词中有几个地方要注意：five fifteen fifty 把ve变成了f再加teen和ty的。four fourteen forty 把our 变成or 再加teen和ty的。
二，序数词
first second third
fourth fifth sixth ...eighth ninth tenth eleventh twelfth thirteenth fourteenth fifteenth twentieth twenty–first twenty-second twenty-third thirtieth fortieth fiftieth sixtieth seventieth eightieth ninetieth one hundredth
注意几点：
第一，第二，第三都是特殊单词；
第四开始都是➕th, 第九去e, 再加th。
第五 ，第十二，把ve 改为f, 再加th
从第二十一开始，把后面的个位数变为序数词即可，如：twenty-first
以ty结尾的数词，一定要记得把y改为i,再加eth三个字母。如：twentieth thirtieth
第100，one hundredth
三，用法 序数词左边要有定冠词the,表示第几
- Sunday is the first day of the week. 星期天是一周的第一天。
- Monday is the second day of the week. 星期一是一周的第二天。
- January is the first month of the year. 一月份是一年的第一个月。
- December is the twelfth month of the year. 十二月份是一年中的第十二个月。
- Today is my cousin's sixtieth birthday.今天是我的表哥第六十个生日。
- March 29, 2024 is my father's ninetieth birthday. 2024年3月29日是我爸的第90个生日。
四，修饰限定有序数词的名词，非谓语动词只能用动词不定式。
- Yang Liwei is the first Chinese astranaut to land on the moon. 杨利伟是中国第一个登上月球的宇航员。
- Mary is the second student to get to school today. 马丽是今天第二个到校的学生。
- Lucy is the fifth girl to give a performance. 露西是第五个表演的女孩。
- Mr. Lee is the first teacher to go abroad for further eduation. 李先生是第一个到国外深造的老师。
五，a ➕序数词 表示又一个
- Yesterday we went to three shops to buy a skirt，but we failed to buy a good one. Then we went to a fourth shop, and we got a very beautiful one. 昨天我们去了三个商店买裙子。但是，我们没有买到好看的裙子。后来，我们又去了一家店，并且买到一件非常漂亮的裙子。
- Mrs. Brown has two children, and last year she had a third son. 布朗太太已经有了两个小孩了，去年又生了一个儿子。
- My sister failed the exam last year. Today he tried a second time. 我妹妹去年考试没有及格，今天她又去试了一下。
- Kate was the first student to hand in her examination paper yesterday.昨天凯特是第一个交卷的学生。
