Key Concept: Vitamins split into two groups by solubility — fat-soluble (A, D, E, K) and water-soluble (the rest).
Why it's correct: Vitamin D is fat-soluble, absorbed with dietary fat and stored in body fat, and plays a key role in calcium absorption and bone health.
Why others fail: Vitamin B12, Vitamin C, and Vitamin B6 are all water-soluble — the body doesn't store them in meaningful amounts, unlike the fat-soluble group Vitamin D belongs to.