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
Object permanence milestone develop at? 
Select and explain. 
A. 6 months, B. 9 months, C. 12 months, D. 15 months
B: 9 months
Answer: B: 9 months 
Explanation: Ans. is 'b' i.e., 9 month