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': 'What is the composition of this stone? \nSelect and explain. \nA. Calcium oxalate monohydrate, B. Calcium oxalate dihydrate, C. Ammonium urate, D. Calcium oxalate', 'role': 'user'}, {'content': 'Answer: B \nExplanation: - Stone has spikes. This stone is known as JACK STONE.- Most commonly found in urinary bladder- Composition is calcium oxalate dihydrate', 'role': 'assistant'}]