This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Biochemistry
Which Fat soluble vitamin is functioning like a "Hormone": 
Select and explain. 
A. Vitamin A, B. Vitamin D, C. Vitamin E, D. Vitamin K
B: Vitamin D
Answer: B: Vitamin D 
Explanation: Vitamin D