We need an apple and a knife.
a boy, a university, a European country
an hour ，an honor ，an island
an elephant， an umbrella， an egg
eg. This is a pencil case.
eg. I met an old man On my way home.
eg. There’s a third boy near the shop.
eg. They have music lessons twice a week.
give a lesson take a bath have a rest
教(一堂)课 洗(个)澡 休息
have a talk have a fever have a good time
听报告 发烧 过得愉快
have(take)a walk have a headache have a nice trip
散步 头疼 旅途愉快
a lot of, a lot, a little, a few, a glass of, such a/an, have a word with, have a look, have a try, have a swim, a quarter, half an hour, three times a day, have a talk, give a talk, ten Yuan a kilo
eg, a bike, an egg
②当名词被such, what, many修饰时，不定冠词放在这些词之后。
eg.It took me half an hour to finish my homework.
He left in such a hurry that he forgot to close the door.
What a dangerous job it is!
Many a man has gone to the big cities for work.
③当名词前的形容词前有so, how, too等词时，不定冠词应放在形容词之后。
Eg. She was so nice a girl that she took the blind man to the station.
How nice a film this is!
④当名词前面有形容词和quite, rather, very时，不定冠词放在quite, rather之后,very之前。
eg.It is quite a good book.
That is rather a useful too1.
This is a very interesting story.