The noun here is non specific and singular, the 'question' could be any question, not a particular one. Hence we use an indefinite article, particularly 'a', since the noun begins with a consonant. Hence the correct option is A. Option B is incorrect because, even though it's an indefinite article, the noun does not begin with a vowel. Option C is incorrect because the noun is not specific nor is it definite. Option D is incorrect because the noun is not an uncountable noun, nor is it a proper noun, and needs an article.