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 difference between a reamer and a file is in: \nSelect and explain. \nA. The number of flutes, B. The number of flutes and shape of the shaft, C. The number of flutes and the size of the shaft, D. The shape and size of the shaft', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]