Final answer:
Vitamin D functions include bone calcification, regulating blood calcium levels, and stimulating osteoclasts for calcium release, making all options given in the question correct.
Step-by-step explanation:
All of the provided options are functions of Vitamin D. Vitamin D is necessary for bone calcification, as it plays an essential role in the absorption of calcium in the digestive tract and its reabsorption in the kidneys, which in turn helps maintain normal serum concentrations of calcium and phosphate. This vitamin also regulates blood calcium levels by working synergistically with parathyroid hormone (PTH) to stimulate osteoclasts when calcium is needed. Moreover, the activated form of vitamin D, calcitriol, is crucial for metabolic processes that ensure proper bone health and density.