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.
theory
Noun
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A theory is an idea that tries to explain an observation.
The new information showed that his theory about growth was incorrect.
Nobody has disproved Einstein's theory of general relativity.
of
Preposition
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Made using.
It is a house of cards.
accounting
Noun
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Accounting involves keeping records on financial information.
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An accounting goes over an event that happened and the explanation for why it happened.