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: Surgery
[{'content': 'Primary bone graft in cleft palate patient? \nSelect and explain. \nA. 6 month - 1 year, B. < 2 year, C. 2-4 year, D. 4-5 year', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]