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': 'Collagen fibrils have a transverse striation with a characteristic periodicity of \nSelect and explain. \nA. 64 cm, B. 64 nm, C. 640 μm, D. 640 nm', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]