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: Pharmacology
25-Dihydroxycholecalciferol is converted to 1,25-dihydroxycholecalciferol in: 
Select and explain. 
A. Skin, B. Lung, C. Liver, D. Kidney
D: Kidney
Answer: D: Kidney 
Explanation: None