This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Gall Bladder & Bile Ducts, Subject name: Surgery
[{'content': 'Regarding stones in gall bladder the following are true except: \nSelect and explain. \nA. Mixed stones are common in the west, B. In Saints triad diverticulosis of colon and hiatus hernia co exist, C. 90% of gall stones are radio-opaque, D. Is a risk factor in the development of GB carcinoma', 'role': 'user'}, {'content': "Answer: C \nExplanation: Ans: c (90% of gall stones are radioopaque)Ref: Bailey & Love, 24th ed, p. 1103, 1104 p. 1095 for 'd' & 23rd ed, p. 975 for 'c'", 'role': 'assistant'}]