Question

At the art fair, he bought an unusual and beautiful gift for his aunt.

Answer 1

The indefinite article is "an"

Hope this helps

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=)

Answer 2

Indefinite articles are the difference between talking about a specific cookie, or any old cookie at all. 

That's the definition for indefinite article, I can't really help you that much, as I don't know the options you have if you post the options I could help you better.