The group A,I,O is a vowel group because all three letters, A, I, and O, are vowels. Vowels are a type of speech sound produced by the vocal cords without any obstruction in the mouth or throat. They are typically represented by the letters A, E, I, O, U in the English alphabet. In this group, B, E, M and W, U, O contain both consonants and vowels, while P, A, V contains two consonants and one vowel. Therefore, the group A,I,O is the only one that consists entirely of vowels.