不定冠詞a/an的用法：
不定冠詞有兩個，a 和 an。a用在輔音開頭的單詞前面;an用于以元音開頭的單詞前。如：a book, an apple。具體用法如下：
1)表示“一個”、“某一個”、“ 每一”、“再一，又一”、或“同一，相同”等
Eg：
Rome is not built in a day.
A Mr. Smith is waiting for you at the school gate.
He usually works eight hours a day.
You can try it a second time if you fail.
They are of an age./ Birds of a feather flocks together.
2)泛指某一類人或物，意為“任何一個，任一”
Eg:
A square has four sides.
3)當物質名詞具體化表示“一(類、陣、份)”等;抽象名詞具體化為“……的人或者事”時
Eg:
Green tea is a wonderful tea.
We don’t have much rain here, but last night we had a heavy rain.
Reading is a pleasure for me.
The meeting is a great success.
4)表示季節、月份、日期、三餐的名詞，或表示世上獨一無二的物體名詞前有形容詞修飾時：
Eg:
We have a every cold winter last year.
This happened on a rain Sunday towards the end of May.
We hope we can see a full moon tonight.
5)源于動詞的名詞與take/have 連用時：
Take a look; take a walk; have a break; have a visit to…