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': 'Reamers and files differ mainly in: \nSelect and explain. \nA. Cross sectional form, B. Colour coding, C. Number of flutes along the blade, D. Instrument formula', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]