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: Medicine
[{'content': 'A 25 year old male presented with pigmentation of nose and pinna. After voiding, his urine becomes dark. His spine is most likely to show - \nSelect and explain. \nA. Atlantoaxial subluxation, B. Spondyloptosis, C. Basilar invagination, D. Calcification of disc', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]