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: Pediatrics
[{'content': 'Object permanence milestone develop at? \nSelect and explain. \nA. 6 months, B. 9 months, C. 12 months, D. 15 months', 'role': 'user'}, {'content': "Answer: B \nExplanation: Ans. is 'b' i.e., 9 month", 'role': 'assistant'}]