This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Urinary bladder, Subject name: Surgery
[{'content': 'The commonest bladder stone is: \nSelect and explain. \nA. Triple phosphate, B. Xanthine, C. Uric acid, D. Cysteine', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Bladder stone Primary bladder stone- Aka Endemic bladder calculi- Most common type of primary bladder stone - Ammonium urate - other stones- Calcium oxalate. Secondary bladder stone - More common in elderly males due to BPH /Bladder outlet obstruction- Most common type of secondary bladder stone - Uric acid> Struvite- Overall secondary bladder stone - most common Investigations- Investigation of choice- Ultrasound Treatment- For small stones - cystolitholapexy- For Large stones* Electrohydraulic lithotripsy* Suprapubic cystolithotomy', 'role': 'assistant'}]