Correct Answer: D

Rationale: Vitamin D is synthesized in the human skin when exposed to ultraviolet B (UV
B) rays from sunlight. This process involves the conversion of 7-dehydrocholesterol into cholecalciferol (vitamin D₃), which is then metabolized by the liver and kidneys into its active form, calcitriol. Vitamin D plays a crucial role in calcium and phosphorus absorption, essential for bone health and immune function. Deficiency in this vitamin can lead to rickets in children and osteomalacia in adults. Regular moderate sunlight exposure is a natural and effective way to maintain adequate vitamin D levels.

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