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': 'Investigation of choice in gall bladder stone is: \nSelect and explain. \nA. USG, B. X-ray abdomen, C. OCG, D. Intravenous cholangiography', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans: a (USG)Ref: Bailey & Love, 24th ed, p. 1097 & 23rd ed, p. 968', 'role': 'assistant'}]