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': 'Gall stones are composed of all except: \nSelect and explain. \nA. Oxalates, B. Bile salts, C. Cholesterol, D. Bile pigments', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans: a (Oxalates)Ref: Bailey & Love, 24thed, p. 1103 & 23rd ed, p. 974', 'role': 'assistant'}]