3) 用于表示价格、速度、比率等名词前，如five pence a kilo, sixty kilometers an hour, four times a day等。
4) 用于下列这样的固定短语中。如a couple, a dozen, half a dozen, a hundred, a lot of, a great many, a great deal of, a large amount/quantity of, a good number of 等。
I’ve done a great deal of work today. (不可数)
What a large number of books you have! (可数)
It’s a good five miles(=at least five miles, perhaps mote) to the station.
5) 以元音开头的单词前不定冠词用an, 如：an apple, an egg, an item, an old man, an umbrella, an hour; 以辅音开头的单词前不定冠词用a university student, a humorous man。
EXERCISE l
A. Put a or an before each of the following:
1. motel (汽车游客旅馆) 2. unusual approach
3. honest boy 4. awkward situation
5. exit (出口) 6. urgent message
7. unique opportunity 8. extremely exciting film
B.Translate the following into English：
1.一座新办公楼 2.一位旅行社代理人
3.一位美国科学家 4.一天的郊游
5.一张印度邮票 6.一次心脏病发作
7.一个先进国家 8.一个有意思的剧本
EXERCISE 2
Fill in the blanks with a or an where necessary:
1. Telephone is very important means of communication.
2. Mothers often tell small children stories before bedtime.
3. I'll pay you thousand year. It’s not enormous salary but after all you are completely unskilled worker.
4. —You’11 get shock if you touch live wire with that screwdriver(螺丝起子). Why don’t you get screwdriver with insulated(绝缘的)handle?
5. — I’m not wage-earner; I’m self-employed man. I have business of my own.
—Then you’re not worker; You’re capitalist!
6. —I have hour and half for lunch.
—I only have half hour — barely time for smoke and cup of coffee.
7. It travels at just under thousand miles hour.
8. I have never known such hot weather.
EXERCISE 3
Insert a or an where necessary:
A.
1. I had very bad night; I didn’t sleep wink (眨眼;打盹).
2. This man has honesty that we all appreciated.
3. Mr. Brown had vision of new and happier Europe.
4. It’s time you had holiday. You haven’t had day off for month.
5. There is hourly service of buses in this route.
6. It is great honour to be invited to such gathering.
7. 1 wouldn’t climb mountain for $ 1, 000! I have horror of heights.
8. Children usually learn the difference between right and wrong at early age.
9. I can’t tell you definitely yet. I'll have word with my wife about it and tell you our decision tomorrow.
10. If boy is not making satisfactory progress at school, his parents should seek advice from his teacher.
B.
1. This is big problem, but not too big problem for us to solve.
2. He had square nose, grey hair and brown skin. She had never seen so handsome man.
3. However great disaster he suffered, John never gave up.
4. Many shipwrecked sailor has been rescued by our brave coastguards(海岸警卫队).
5. Such urgent need requires prompt action.
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