Option A is the correct answer. In simple language, a consonant is a speech sound that is not a vowel. So we can say that non- vowel sounds are consonants. We can say that articles mean the words A, An, and The. "An" is used before nouns in singular numbers that start with vowels{A, E, I, O, U}. It can also occur before countable nouns in the singular number with a vowel sound(Eg. An hour). 
Article "A" takes place with countable nouns in singular numbers that begin with consonants(Eg. A car)