The correct article to complete the sentence is "an." This is because "an" is the indefinite article used before a word that starts with a vowel sound. In this case, the word "elephant" starts with a vowel sound, "e", so "an" should be used.

The article "a" is not correct because it is used before words that start with a consonant sound.

The article "the" is not correct because it is used to indicate a specific noun that is being referred to.

No article is not correct because it is not used before a singular count noun.