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: Radiology
[{'content': "Frostburg's reverse 3 sign is seen in – \nSelect and explain. \nA. Periampullary carcinoma, B. Annular pancreatic carcinoma, C. Carcinoma head of pancreas, D. All", 'role': 'user'}, {'content': 'Answer: C \nExplanation: Reversed \'3\' sign of frost berg\xa0\xa0→\xa0Carcinoma head of pancreas.\nDouble duct sign\xa0→\xa0Periampullary carcinoma.\n"Beaded appearance" of biliary ducts\xa0→\xa0Primary sclerosing cholangitis.', 'role': 'assistant'}]