Used before nouns and noun phrases that denote a single but unspecified person or thing.
예문
1. Rome was not built in a day. (로마는 하루아침에 이루어지지 않았다) 2. A Mrs. Johnson has come to see you. (존슨 부인이라는 분이 당신을 찾아왔습니다) 3. in a sense (어떤 의미로는) 4. I have a knowledge of English. (영어에 관해서 조금은 알고 있다) 5. for a week (1주간)
