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DET
（指初次提及或非特指的人或物）一（个）
You use a or an when you are referring to someone or something for the first time or when people may not know which particular person or thing you are talking about.
例句
A waiter entered with a tray...
侍者端着托盘进来了。
He started eating an apple...
他开始吃苹果。
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DET
（一类人或事物中非特指的）任何一（个）
You use a or an when you are referring to any person or thing of a particular type and do not want to be specific.
例句
...expensive make-up that we saw being advertised by a beautiful model...
我们所见的由一位漂亮模特代言的昂贵化妆品
I suggest you leave it to an expert...
我建议你把它留给专家来解决。
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DET
（用于前加形容词或后加修饰语的不可数名词之前）一（种）
You use a or an in front of an uncount noun when that noun follows an adjective, or when the noun is followed by words that describe it more fully.
例句
There was a terrible sadness in her eyes...
她眼神中流露出深深的悲伤。
He did have a real knowledge of the country...
他对该国的确知之甚多。
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DET
（用于物质名词前）一（类），一（种）
You use a or an in front of a mass noun when you want to refer to a single type or make of something.
例句
Bollinger 'RD' is a rare, highly prized wine.
博林格RD香槟是一种名贵的备受推崇的葡萄酒。
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DET
（用于表示数量的词组中）许多/少许/一点
You use a in quantifiers such as a lot ,a little, and a bit.
例句
I spend a lot on expensive jewelry and clothing...
我花很多钱购买昂贵的首饰和衣服。
I've come looking for a bit of advice.
我特来讨教。
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DET
（一类人或事物中典型的）一（个）
You use a or an to refer to someone or something as a typical member of a group, class, or type.
例句
Some parents believe a boy must learn to stand up and fight like a man.
有些父母认为男孩子必须学会像男子汉一样顶天立地，勇于抗争。
...the operation a patient has had.
病人做过的手术
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DET
（用于日子、月份或节日的名称之前以表示特例）一个
You use a or an in front of the names of days, months, or festivals when you are referring to one particular instance of that day, month, or festival.
例句
The interview took place on a Friday afternoon...
采访是在一个星期五的下午进行的。
It was a Christmas when shoppers passed by expensive silks in favor of more practical gifts.
这是一个购物者不理会昂贵的丝绸衣服而热衷于更实用礼物的圣诞节。
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DET
（从事某一职业的）一（位），一（名）
You use a or an when you are saying what someone is or what job they have.
例句
I explained that I was an artist...
我解释说自己是个艺术家。
He was now a teacher and a respectable member of the community.
他现在是一位教师，并且是社区内受人尊敬的一员。
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DET
（用于不为说话人所知的首次提到的人名前）某一（个）
You use a or an in front of the names of people as a way of indicating that you do not know them or anything about them and you are saying their name for the first time.
例句
The full address on a stick-on label was that of a Mrs P. R. Slater of Peterborough...
不干胶标签上的完整地址写的是彼得伯勒的一位P. R. 斯莱特太太。
A Dr Matthew Owens was reported missing while on an expedition to north-eastern Turkey.
据报道，一位叫马修·欧文斯的博士在前往土耳其东北部考察的途中失踪了。
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DET
（用于人名前，表示与该人有相同特性或品质）类似…的一个（或一位）
You use a or an in front of the names of people when you want to refer to someone else who has the same qualities or character as the person named.
例句
When I listen to her play I can hear a new Nigel Kennedy.
从她的演奏中我听出了新一代的奈杰尔·肯尼迪。
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DET
（用于姓氏前，表示某人属于某姓氏家族）一位姓…的人
You use a or an in front of a surname when you want to refer to someone who belongs to the family with that surname.
例句
As far as I can recall, Patti was a Smith.
我记得帕蒂是姓史密斯的。
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DET
（用于艺术家名字前）一幅…的画，一件…的雕塑作品
You use a or an in front of the names of artists to refer to one individual painting or sculpture created by them.
例句
Most people have very little difficulty in seeing why a Van Gogh is a work of genius.
多数人不难理解为什么凡·高的作品是天才之作。
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DET
（代替数字one使用，尤用于hundred，hour和metre等表示度量的单词之前以及half, quarter和third等分数之前）
You use a or an instead of the number 'one', especially with words of measurement such as 'hundred', 'hour', and 'metre', and with fractions such as 'half', 'quarter', and 'third'.
例句
...more than a thousand acres of land.
1,000多英亩地
...a quarter of an hour...
一刻钟
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DET
（用于表示比率的短语中）每一
You use a or an in expressions such as eight hours a day to express a rate or ratio.
例句
Prices start at ￡13.95 a metre for printed cotton...
印花棉布以每米13.95英镑的价格起售。
The helicopter can zip along at about 150 kilometres an hour.
该直升机能以每小时150公里左右的速度疾进。