English grammar rule En a vs an
The plane left a hour ago.
If a word starts with a consonant sound, A is used. An is used before words starting with vowel sounds. It doesn't matter if the word is an adjective, a noun, an adverb, or anything else; the rule is exactly the same.
Examples of 'En a vs an' rule
Incorrect I had an fun time last night. Correct I had a fun time last night.
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