Arficles
1. 辅音音素开首的词前用a,在元音音素前用an
a B.A. (学士)，    an M. A. (硕士)，a 500-meter-wide bridge, an 800-meter-wide river
2.one 与 a 区别:
  a 与 one 同源, a 属one 的弱式; one 强调数目概念,要重读. 注意下列各句的a., one 细微差异.
  It will take more than a year to build the power station .(指一年以上.两年以下)
  It  will take more than one year to build the power station.(指不止一年,可能两年.三年)
  The thing will collapse at a blow. (一打就垮. a并不强调一次这意)
  The thing will collapse at one blow.(打一下准垮. 意即: 不须两下.三下.)
3. a / an 表示 “同一.相同”的概念
Your shoes and mine are of a size .(属同一尺寸, 同一规格)
Christina and I are mealy of an age.  (同龄)
These swords are all of a length.(同样长)
Birds of a feather flock together. 物以类聚, 人以群分.
4 定冠词the用来加强特指意义,表示 “恰恰是,最典型的,最适合的.最理想的.最值得歌颂的”等意思
  This is the word to be used here.(最恰当的字眼)
  Aspirin is the medicine for headache.治头痛的良药
  This is the drink for hot weather.(最理想的饮料)
  John is the man for the job.(最合适的人选)
  This is the life for me (很有意义的生活.)
5.定冠词the用于单数可数n.前表示其属性.功能或与之有关的事物的抽象概念等:
He is at home in the saddle. (riding)(他骑马很内行)
There is still much of the schoolboy in him. (他身上还有十足的学生味)
When did you go on the stage?(当演员)
Peter is too fond of the bottle.(喝酒)
The child is brought up on the bottle.(喂牛奶长大的)
6. 使用零冠词的情况:
①. 物质名词前的零冠词,表示物质的种类.或泛指物质的不定的量: 例如
Water is transformed into steam by heat.
但: 如果物质名词带有限制性修饰语,或整个情景或上下文使这个名词只表示这种物质的某一特定部分时, 则要用定冠词:
The snow before the window has melted.
The steal produced in our plant is of high quality.
如果表示 “一种.一阵. 一场 一份或一个具体情况等概念时通常用不定冠词:
A heavy rain, a good butter(一种优质黄油)
A famous Chinese wine ,  a tomato soup(一份)
②抽象名词前用零冠词表示一般概念
Dose she like music?
  当抽象名词后面有限制性修饰语,特别是of结构,或上下文和整个情景使抽象名词具体化时,要用定冠词:
Phonetics is the science of speech sounds.
如果要表示某抽象名词所代表的概念的 “一种.一类, 一方面,这种,那种”等意义,可用不定冠词:
Physics is a science.
③家庭成员或nurse, cook 等名词前用零冠词:
Aunt is taking Sister out for a walk.
④表示日常饮食名词前:She arrived at supper.
⑤季节名词前:in Spring
⑥介词at, in , to 等连用的某些组织名称或机构名称以及home, town等名词前:
bed, church, prison, hospital, school, class, home, town, sea
⑦ 与by连用交通工具名词前:
by train / bus / plane / sea / water / ship / air / car,etc.
⑧表抽象或一般意义的时间词前:
at dawn / daybreak / dusk / night / noon / sunset / sunrise / twilight / midnight
⑨系词 turn,go(变成)后面作补语的名词前:
She turned traitor in the thirties. (三十年代)
He has gone socialist.
⑩呼语,及表示感叹意味的词之前
Stay where yon are, girl.
⑾as,though, that 引起的让步从句中:
Child as he is, we can’t fool him.
⑿单数可数n.用作紧密联系的并列结构或作列举之用时,用零冠词:
The thief was bound hand and foot.
from head to foot, serve the people heart and soul,
We are brother and sister.
Arm in arm, hand in hand, face to face. From right to left, day after day, time after time, from hand to mouth(现挣现吃地, 仅够糊口地)
⒀ 若干[屏蔽]结构中,用零冠词:
The old man was sitting in a chair, pipe in mouth.
He sat at the table, coat off, head down, gun in hard.
⒁ 头衔, 独一的官员:
She was elected monitor of our class.
As mayor of this city, it is my honor to welcome you