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.
significant
Adjective
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If something is significant, it is important, or large, enough to pay attention to or to believe.
There was a significant drop in the price of gas today, causing drivers to line up at the pumps to fill up.
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A significant look, movement, etc. is one that has a particular meaning.
obstacle
Noun
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An obstacle is something that blocks your way.