This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Kidneys and Body Fluids, Subject name: Physiology
25(OH) cholecalciferol is converted to 1,25-dihydroxy - cholecalciferol in: 
Select and explain. 
A. Skin, B. Lung, C. Liver, D. Kidney
D: Kidney
Answer: D: Kidney 
Explanation: Ans. D KidneyRef: Ganong, 23rd ed. pg. 674