Answer:
"an"
Step-by-step explanation:
Articles
In English, there are two types of articles: The definite article which it's "the" and may be used with singular or plural noun, and the Indefinite articles which are "a" and "an" that may be used with a singular noun.
The indefinite articles mean the same, their difference lies in when to use them: When the article is before a word that begins with a consonant sound, "a" is used, and when the article is before a word that begins with a vowel sound, "an" is used (Such as it is used in the sentence: "an unusual and beautiful gift".