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': 'Most common gall bladder stone is? \nSelect and explain. \nA. Pigment, B. Cholesterol, C. Oxalate, D. Oxalate', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Cholesterol REF: Harrison\'s 17th ed chapter 305 Gallstones are formed because of abnormal bile constituents. They are divided into two major types: Cholesterol stones account for 80% of the total, with pigment stones comprising the remaining 20%. Cholesterol gallstones usually contain >50% cholesterol monohydrate plus an admixture of calcium salts, bile pigments, proteins, and fatty acids, the latter in "brown" pigment stones. Pigment stones are composed primarily of calcium bilirubinate; they contain <20% cholesterol and are classified into \'black" and "brown" types, the latter forming secondary to chronic biliary infection.', 'role': 'assistant'}]