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': 'The root canal instrument most likely to break during instrumentation is \nSelect and explain. \nA. H-file, B. K-file, C. Reamer, D. Pathfinder', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]