The correct answer is d) storage of water.
While the skin performs many vital functions, such as serving as a barrier against microorganisms, producing vitamin D upon exposure to sunlight, regulating body temperature through sweat and blood flow, and preventing dehydration by minimizing water loss, it does not have a primary role in storing water. Instead, the skin helps maintain hydration levels in the body, but it does not function as a storage site for water like other organs, such as the kidneys, do. Therefore, option d is the correct choice as it is not considered a direct function of the skin.