Which is a correct way to build a vowel-set in Python (matching the chapter's spirit)?

• avowels = ['a', 'e', 'i', 'o', 'u', 'A', 'E', 'I', 'O', 'U']
• bvowels = (a + e + i + o + u)
• cvowels = aeiou
• dvowels = "vowels"