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
Collagen fibrils have a transverse striation with a characteristic periodicity of 
Select and explain. 
A. 64 cm, B. 64 nm, C. 640 μm, D. 640 nm
B: 64 nm
Answer: B: 64 nm 
Explanation: None