This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Kidney and ureter, Subject name: Surgery
[{'content': 'Most common renal stone: \nSelect and explain. \nA. Calcium oxalate stone, B. Uric acid stone, C. Staghorn calculi, D. Cysteine stone', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Calcium oxalate MC type of kidney stone (85%) Risk factor are hypercalciuria, hypercalcemia, hyperoxaluria Have hard, small and jagged surface. On section-wavy concentric laminae', 'role': 'assistant'}]