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': 'To avoid external transportation of the root canal \nSelect and explain. \nA. precurve instruments., B. use large instruments., C. avoid the use of sodium hypochlorite., D. use vigorous instrumentation.', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]