1.used when you are mentioning a person or a thing for the first time, or when the person listening to you does not already know about them
2.used when you mean any person or thing of a particular type, but you are not referring to a specific one
3.used when you say what class, type, or group someone or something belongs to, or what job someone has
4.used before a singular noun that represents every person or thing of a particular type
5.used when you are referring to a person or thing as one of several people or things of this type
6.used in expressions of quantity such as “a lot,” “a few,” or “a great deal”
7.used in numbers and measurements to mean “one,” as in “a thousand” or “an hour”
8.used in phrases showing how much something costs, how often it happens, how fast it goes, etc.
9.used before a noun that means a substance, product, food, etc. when referring to a particular type of it
10.used before the name of some drinks to mean a cup or glass of that drink
11.used before a noun that means a particular quality or feeling when the quality or feeling is described in some way
12.used before a noun that is formed from a verb and means a single action of that verb
13.used before a noun that expresses your feelings about a situation
14.used before the name of a particular day, season, or holiday to mean one particular Tuesday, summer, Christmas, etc.
15.used before a person’s name when you do not know anything about them; used before the name of a famous artist to mean a picture by that artist; used before a family name to mean a member of that family; used before the name of a famous person to mean someone else with similar abilities, a similar appearance, or a similar personality
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