The answer is never because this translates into nunca. So this is an adverb of time. Adverbs of time give information on time, duration, and frequency answering questions like <em>When? </em>and <em>How often?</em> Recall that an adverb is a word or group of words that describes or modifies a verb, adjective, another adverb or a whole sentence. So <em>I never eat red meat (Yo nunca como carnes rojas).</em>