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
By what age, does the child develops the following developmental milestone? 
Select and explain. 
A. 8 months, B. 9 months, C. 10 months, D. 12 months
B: 9 months
Answer: B: 9 months 
Explanation: This is Object Permanence - Develops by 9 months of age.
When the baby loses object while playing. Knows that it is somehwere around.