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': 'All are radiolucent stones except \nSelect and explain. \nA. Triamterene stones, B. Uric acid stone, C. Xanthine stones, D. Cystine stones', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Mnemonic - TIXU Triamterene Indinavir Xanthine Uric acid Radiolucent stones', 'role': 'assistant'}]