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: Medicine
[{'content': 'Best diagnosis of pancreatic cancer (head) is by - \nSelect and explain. \nA. Ultrasound, B. ERCP, C. CAT scan, D. PTC', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]