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.
caution
Noun
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Caution is being careful and planning ways to avoid danger or being hurt.
He used caution as he climbed the old wooden steps.
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A caution is a warning about what might happen in the future.
The doctor gave me a caution about eating too much.
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A caution can be a legal warning and that a repeat of the action could end up as an arrest.
The police gave the boy a caution after he was caught stealing from the shop.
caution
Verb
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To caution is to give a warning or advice.
His mother cautioned him about staying out too late at night.