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.
textbook
Noun
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A textbook is a book that is used in school, university, or college to study an academic topic.
I had to bring my math textbook home so I could do my homework.
header
Noun
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A header is the text at the very top of the page.
I put my name and the page number in the header of my term paper.
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In football, a header is a goal scored by hitting the ball with one's head
Peter Crouch's header against Chelsea made the highlight show last night.