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 for obstructive jaundice: \nSelect and explain. \nA. CXR, B. USG, C. CT, D. MRI', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Ans: b (USG) Ref: Bailey, 24thUSG is the first investigation in a case of obstructive jaundice for visualising gall stones, liver tumours, dilated bile ducts.ERCP is the gold standard for CBD stones as it provides therapeutic option at the time of diagnosis.', 'role': 'assistant'}]