a |an 1 指一类人或事，相当于a kind of.A plane is a machine that can fly.2 第一次提及某人某物，非特指。There is a tree in my garden. 3 用于人名前，表示不认识此人或与某名人有类似性质的人或事. Hello, could I speak to Mr. Smith?Sorry, wrong number. There isnt_ Mr. Smith here.A. 不填 B. a C. the D. one4 用于抽象名词具体化的名词前success(抽象名词)a success(具体化) 成功的人或事a failure 失败的人或事 a shame 带来耻辱的人或事a pity 可惜或遗憾的事 a must 必需必备的事5 用于quite, rather, many, half, what, such之后.This room is rather a big one. the 1 表示某一类人或物. In many places in China, the bicycle is still a popular means of transportation. 2 表示说话双方都了解的或上文提到过的人或事. Bring me the book, please. 3 用于世上独一无二的事物名词前. The moon, the earth 4 用于序数词和形容词副词比较级最高级前He is the taller of the two children. 5 用于国家党派等以及江河湖海，山川群岛的名词前the United States, the Communist Party of China, the French.6 表示“一家人”或“夫妇”.Could you tell me the way to the Johnsons, please?Sorry, we dont have a Johnson here in the village.