Which of the following article can be used in this sentence, before the word 'hour': "Hurry up, we are already _ hour late"?

An article is a type of determiner used before a noun, and it defines whether a noun is specific or not. An article can be broadly divided into an indefinite article ("a" and "an") and a definite article ("the"). In the given question statement, an indefinite article will be used. More specifically, "an" will be used. "An" is used when the noun begins with a vowel sound, and the word 'hour' also begins with a vowel sound.