2.1 不定冠詞的用法
冠詞是虛詞,本身不能單獨(dú)使用,也沒有詞義,它用在名詞的前面,幫助指明名詞的含義.英語(yǔ)中的冠詞有三種,一種是定冠詞（the Definite Article）,另一種是不定冠詞（the Indefinite Article）,還有一種是零冠詞（Zero Article）.
不定冠詞a (an)與數(shù)詞one 同源,是"一個(gè)"的意思.a用于輔音音素前,一般讀作[e],而an則用于元音音素前,一般讀做[en].
1) 表示"一個(gè)",意為one；指某人或某物,意為a certain.
A Mr.Ling is waiting for you.
2) 代表一類人或物.
A knife is a tool for cutting with.
Mr.Smith is an engineer.
3) 詞組或成語(yǔ).
a little / a few / a lot / a type of / a pile / a great many / many a / as a rule / in a hurry / in a minute / in a word / in a short while / after a while / have a cold / have a try / keep an eye on / all of a sudden