This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Calcium Metabolism, Subject name: Physiology
Which one of the following vitamins stimulates calcium absorption by the GI tract? 
Select and explain. 
A. Vitamin E, B. Vitamin D, C. Vitamin A, D. Vitamin K
B: Vitamin D
Answer: B: Vitamin D 
Explanation: Ans. B. Vitamin DVitamin D plays an important indirect role in the absorption of calcium by the GI tract. The other vitamins listed are not involved in the absorption of calcium.