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': 'What is more appropriate for diagnosis of CBD stones \nSelect and explain. \nA. Ultrasonography, B. ERCP, C. O C G, D. IV cholangiography', 'role': 'user'}, {'content': 'Answer: B \nExplanation: USG is the first investigation\nMRCP is the best non-invasive investigation\nERCP is the gold standard for diagnosing CBD stones. It has the advantage of providing a therapeutic option at the time of diagnosis.', 'role': 'assistant'}]