a / an 区分 a useful book / a one-eyed camel / a European village / a uniform / a university a usual thing an unusual thing / an hour / an umbrella / an honest boy / an English book an apple / an eight-year-old boy / an unhappy boy 26个英文字母单独使用时，泛指前an的字母是：Mr. Li has one fox. 例如：There is an o in the word worry .
