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: Pathology
[{'content': 'Onion skin" fibrosis of bile duct is seen in? \nSelect and explain. \nA. Primary biliary cirrhosis, B. Primary sclerosing cholangitis, C. Extrahepatic biliary fibrosis, D. Congenital hepatic fibrosis', 'role': 'user'}, {'content': "Answer: B \nExplanation: Ans. is 'b' i.e., Primary sclerosing cholangitis", 'role': 'assistant'}]