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: Orthopaedics
[{'content': "All of the following show genu recurvatum, except \nSelect and explain. \nA. Perthe's disease, B. Rheumatoid arthritis, C. Poliomyelitis, D. Rickets", 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]