The indefinite articles 'a' and 'an' are used when the noun is singular, non-specific or one of many. In the given statement, volleyball is one of many sports, hence an indefinite article would be used before the noun 'sport'. 'A' precedes the non-specific noun that begins with a consonant. The article here is placed before the phrase 'very good sport', hence we don't consider the initial of the noun, but the initial of the adverb 'very', which begins with the consonant 'v' hence option A is correct. Option B is incorrect because the noun, in this case the adverb, does not begin with a vowel. 'The' is used when the noun is specific since we are not referring to a specific volleyball match, it's incorrect here. An article is omitted when the noun is uncountable, plural, or a proper noun, since the noun 'sport' is countable, singular and it's not a proper noun, option D is not used and it's incorrect.