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: Surgery
Prostate calculi are usually composed of 
Select and explain. 
A. Calcium carbonate, B. Calcium phosphate, C. Calcium oxalate, D. Cystine
B: Calcium phosphate
Answer: B: Calcium phosphate 
Explanation: None