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': 'In poliomyelitis which part of spinal canal is involved: \nSelect and explain. \nA. Anterior horn, B. Lateral horn, C. Posterior horn, D. Medial horn', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]