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': 'Technique of root canal preparation known as telescopic technique is \nSelect and explain. \nA. Crown down, B. Conventional step down, C. Conventional step back, D. Step back pressure Less', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]