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: Physiology
Which of the following organ is not involved in calcium metabolism: 
Select and explain. 
A. Lung, B. Liver, C. Spleen, D. Skin
C: Spleen
Answer: C: Spleen 
Explanation: C i.e. Spleen