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': 'Most common epicenter of a radicular cyst is: \nSelect and explain. \nA. Distal surface of tooth, B. Apex of tooth involved, C. Mesial surface of tooth, D. Deep periodontal pocket', 'role': 'user'}, {'content': 'Answer: B \nExplanation: In most cases, the epicenter of a radicular cyst is located approximately at the apex of a nonvital tooth. It occasionally appears on the mesial or distal surface of a tooth root at the opening of an accessory canal or infrequently in a deep periodontal\xa0pocket.\xa0\nOral radiology White and Pharaoh; 7th ed. Page no 335', 'role': 'assistant'}]