I’ve been waiting for __________ long time.

Answer: a

Use "a" before singular, countable nouns (or noun phrases) that begin with a consonant sound. In the sentence, the word "long" begins with the consonant sound /l/, so the correct phrase is "a long time."

• "an" is used before words that begin with a vowel sound (for example, "an apple").

• "the" is the definite article and is used when referring to something specific or already known (for example, "the last time").

• No article is not standard here; the natural, standard form is "I've been waiting for a long time."