英语语法入门：不定冠词a&an

英语自学网

1. We use the indefinite article, a/an, with count nouns when the hearer/reader does not know exactly which one we are referring to:当听的人或者读者不清楚我们确切指得是哪个的时候，我们用不定冠词a/an来形容可数名词：
        Police are searching for a 14 year-old girl.
        2. We also use it to show the person or thing is one of a group:我们也可以用来表示该人或物是同一组：
        She is a pupil at London Road School.
       

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        3. We do not use an indefinite article with plural nouns and uncount nouns:我们不用不定冠词来修饰复数或者不可数单词：
        She was wearing blue shoes. (= plural noun)
        She has short blonde hair. (= uncount noun)
       

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        4. We use a/an to say what someone is or what job they do:我们用a/an描述他人的工作：
        My brother is a doctor.
        George is a student.
        5. We use a/an with a singular noun to say something about all things of that kind:我们用a/an形容一个单数名词来表示一类事物：
        A man needs friends. (= All men need friends)
        A dog likes to eat meat. (= All dogs like to eat meat)