The correct option is A moderate
Extreme means reaching a high or the highest degree; very great. The opposite of extreme is moderate, or average in amount, intensity, quality, or degree. Hence, Option B is correct. Among the rest of the options, refined means elegant and cultured in appearance, manner, or taste, plain means elegant and cultured in appearance, manner, or taste, ordinary means with no special or distinctive features. These options do not express the intended antonym, hence incorrect.