'A' is an indefinite article which is usually used before a noun which begins with a consonant, is singular and it's the first time that the noun is being spoken about, making Option B the correct answer. The article 'an' is used when the noun begins with a vowel, and is spoken about for the first time. Since the noun in the statement does not begin with a vowel, Option A is incorrect. The article 'the' is used for specific nouns, either singular or plural, and have been spoken about earlier. The noun in the given statement seems to have been mentioned for the first time in front of the 2nd person, hence 'the' is not the correct answer. Articles are not required when generalizing about uncountable nouns, plural countable nouns and sometimes even singular nouns (Though, not in the given sentence). Since the noun in the statement is a singular noun, Option D is incorrect.