|用于可数名词单数形式前||Susan is a scientist.
Pass me an orange, please.
|不特指某人或某物||A boy is looking for you.
We work five days a week.
|表示“一”的数量，但没有one强烈||We are going to have an English lesson tomorrow.
I have a mouth, a nose, two eyes and two ears.
|用于固定词组中||A few, a little, a lot of, a moment ago|
|特指某人或者某物||Show me the photo of the boy.|
|双方都知道的事物或人||Where are the new books, Jim?
They are on the small table.
|上文提过的人或物||Ji Wei lives on a farm. The farm is not big.|
|独一无二||The sun is bigger than the moon.|
|序数词和形容词最高级前||The first month of the year is January.|
|普通名词构成的专有名词前||The Great Wall|
|习惯用语||In the morning
On the left