冠词：冠词是置于名词之前，对名词起限制作用的一种虚词。
说明名词所表示的人或者事物的词，主要放在名词之前，它不能离开名词而单独存在。冠词分为不定冠词（a, an），定冠词（the），和零冠词（名词前不用冠词）。
不定冠词有a和an两种形式。a用在以辅音音素开头的单词前， an用在以元音音素开头的单词前。
即：
a 辅音音素开头单词
an 元音音素开头单词
不定冠词的具体用法：
1. 以a, e, i, o开头单词一般加an(特殊：one和European)。
one和European 的发音是辅音音素开头，所以前面也是需要用不定冠词a。如：
a one-hour trip，一位欧洲人：a European.
2.以u开头的单词要看发音，
u的发音有两种：
发/ju:/时， 单词前用a (useful, university, unit, )
发/ ʌ/时， 单词前用an (umbrella, ugly, uncle, unusual)
3.h开头但h不发音的单词，记住三个常考的特例：hour, honest, honor等，用an。
4.单独字母前的a和an的选用请记住一句话：Mr. Li has one fox. 字母在这句话里面的用an，不
在里面的用a。
所以以下12个字母（A/a, E/e, I/e, O/o, F/f, H/h, L/l, M/m, N/n, S/s, X/x, R/r）前用an来限
定。如：There is an “m”, an “a” and a “c” in the word “mice”.
5. 需要注意数字所代表的英文单词的首个音素的发音。
an 11-year-old boy, an 18-year-old girl.
6.''a 序数词''表示“又一，再一”（常考难点）。
比如：The man had two houses in the city, and he bought a third one.区别：定冠词（the） 序数词 表示''第几''的意思
还有几个需要注意的考点：
相关练习：
( )1. Tom is ______ boy. He is ______ American boy.
A. a; a B. an; a C. a; an D. a; /
( )2. ______horse can help people carry heavy things.
A. The B. A C. An D. /
( )3. China is______ old country with ______long history.
A. the; a B. a; an C. an; a D. an; the
( )4. There is______ 800-meter-long bridge over the river.
A. a B. An C. the D. /
( )5. Have you got______ e-mail? I want to e-mail you some photos.
A. a B. an C. the D. /
( )6.---What do you think of Lucy?---She is ________ honest girl.
A. an B. a C. the D. /
( )7.As Tim loves Xiamen a lot, he bought ___ one way ticket to Xiamen and decided to stay there for a year.
A. an B. a C. / D. the
( )8.Do you know a spaceship that flies at about nineteen kilometers ________ second?
A. the B. a C. / D. an
( )9.---You have dropped___ ''s'' in the world necessary.
---Oh, ____letter “s” is doubled.
A. a; a B. a; the C. an; the D. the; the
( )10.Miss Zhang will go to ________ America for ________ important meeting next month.
A．an; an B．/; an C．/; a D．an; the
答案：1-5CBCBB 6-10 ABBCB
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