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
[{'content': 'Percentage of gall stones which are radio opaque ? \nSelect and explain. \nA. 10%, B. 20%, C. 30%, D. 50%', 'role': 'user'}, {'content': "Answer: A \nExplanation: Ans. is 'a' i.e. 10%", 'role': 'assistant'}]