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: Dental
[{'content': 'Location of root canals is best done by endodontic \nSelect and explain. \nA. Probe, B. Explorer, C. Ultrasonic system, D. File', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]