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在学完定语从句之后，同学们会接触到的另一个语法项目是数词。表示数目、多少和顺序先后的词叫数词。数词有两种：表示数目多少的数词叫基数词，如：one，ten twenty-three；表示顺序先后的数词叫序数词，如：first，third，twentieth。
1.基数词
基数词相当于名词，在句中可做主语、表语、定语、状语等。如：
Three of my classmates are from Shanghai.
I am twenty this year.
They have four classes in the morning and three in the afternoon.
2.序数词
1)序数词的构成：
★大多数的序数词是由基数词加-th构成。如：seven—seventh；ten—tenth
★以-t结尾的基数词只在词尾加-h。如：eight—eighth
★以-ve结尾的基数词改-ve为f再加-th。如：five—fifth；twelve—twelfth
★以-y结尾的基数词改-y为-ie再加-th。如：twenty—twentieth，thirty—thirtieth
★几十几的序数词只在个位数体现。如：twenty-one—twenty-first；thirty-three—thirty-third
★特殊的序数词：
one—first；two—second；three—third； nine—ninth
2)序数词在句中同样可做主语、表语、定语、状语等。如：
June the first is Children’s Day.
When did you first meet each other?
She was the last to arrive.
3.数词的用法：
1)表示年、月、日，“年”用基数词，“日”用序数词。如：May eleventh，2007
2)表示时间。如： It’s eleven twenty.
3)表示编号。编号既可以用基数词表示，也可以用序数词表示。区别是基数词用在名词之后，序数词位于名词之前，并加定冠词。如：Lesson Nine；the Ninth Lesson
4)介词in one’s+整数数词的复数形式，表示年龄。如：
She is in her early forties.(她四十出头。)
5)序数词前加冠词“a”表示“再一次”。如：Can I try a second time?
6)在hundred，thousand，million，billion前有数词时为实数意义，它们的词尾不能加复数。前无数词时为虚数意义，hundred，thousand，million，billion可加复数，并可和of连用，构成短语。如：five hundred students；millions of people
4.分数的构成
分子用基数词，分母用序数词，分子大于1时，分母加s，如：
1/5：one fifth
2/3：two thirds
2-：two and three quarters
5.小数的表示法
0.09：point zero nine
2.7：two point seven
6.百分数的表达法
90%：ninety percent
0.5%：point five percent
7.倍数表达法
表示两倍时用twice，表示三倍以上的倍数时用times。如：
The earth is 49 times the size of the moon.
This desk is twice as large as that one.
8.算式表达法：
5+6：five plus six(or five and six)
7-6：seven minus six
2×3：two multiplied by three(or two times three)
8/4：eight divided by four
9.与数词相关的主谓一致原则
1)当名词词组中心词为表示时间、路程、金钱或重量等复数名词时，往往根据意义一致的原则，把这些复数名词看做一个整体，谓语采用单数形式。如：
Twenty dollars is not enough.
Two months has passed before we realized.
但是如果“数词”单用，表示人或物，谓语动词一般用复数。如：
Three were killed and ten were missing in that accident.
2)如果名词词组中心词是“分数或百分数+of-词组”，谓语动词的单、复数形式取决于of-词组中名词或代词的单、复数形式：如果of-词组中名词或代词是单数或不可数名词，谓语动词用单数形式；如果of-词组中名词或代词是复数，谓语动词也用复数形式。如：
Two thirds of the earth is covered with water.
Two thirds of the people present are against the plan.
3)如果主语是many a，more than one+单数名词构成，尽管从意义上看是复数，但谓语动词仍用单数形式。如：
Many a student in this class has hoped a long break.
4)a+单数名词+or two做主语，谓语动词用单数形式。如one or two+复数名词，谓语动词用复数形式。如：
A word or two is missed in the sentence.
One or two words are missed in the sentence.
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