used before a noun to talk about one person or thing not mentioned before
I need a pen to write a letter.
我需要一支筆來寫一封信。
used to show someone is part of a group or has a job
He is a doctor at a hospital.
他是一家醫院的醫生。
any or every one of something
A cat has a tail and a good sense of balance.
貓有尾巴和良好的平衡感。
used before a feeling or idea word that has a describing word
She felt a deep sadness after a loss.
在一次損失後,她感到深深的悲傷。
used before two things that go together
Please bring a plate and a cup for the party.
請為聚會帶一個盤子和一個杯子。
used instead of 'one' before some numbers
About a hundred people came to a meeting.
大約一百人參加了一個會議。
used when talking about how much things cost or how many
Apples cost two dollars a pound at a market.
在一個市場上,蘋果每磅兩美元。
a person who is like someone else
My brother is a real Einstein when it comes to a puzzle.
當涉及到謎題時,我哥哥真是個愛因斯坦。
used before a name to show you don't know the person
There is a Mr. Smith waiting to see you in a room.
有一位史密斯先生在一個房間裡等著見您。
used before a day to talk about one specific day
We always have a meeting on a Monday at a set time.
我們總是在某個星期一的固定時間開會。