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.
period
Noun
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A period is a length of time.
There was a short period when my computer stopped working.
During the first period, Germany scored two goals.
The dinosaurs lived from late in the Triassic period (about 225 million years ago) until the end of the Cretaceous (about 65 million years ago).
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A period is the dot that marks the end of most sentences in English. This -> . is a period.
Should I use an exclamation mark or a period at the end of this sentence?
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A woman's period is the time each month when she passes blood.
I have missed two periods now. I think I must be pregnant.
period
Interjection
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And nothing else; and nothing less; used for emphasis.
When I say "eat your dinner," it means "eat your dinner", period!