Englishfor English speakers
a
Determinative
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A is used when the following word could be any of a certain type.
Compare "A book I saw on the shelf" and "The book I gave you yesterday".
a
Noun
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A is the first letter of the alphabet.
The letter "a" comes before "b".
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In some schools, an A is a very high grade.
Ron got an A on his earth science test.
appointment
Noun
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A formal agreement to meet or visit someone (for example, a doctor) at a certain time and place.
I have a doctor's appointment at 3:00 tomorrow.
Let's make an appointment for lunch on Tuesday next week.