This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Social and Language Milestones, Subject name: Pediatrics
A 3 month baby can do: 
Select and explain. 
A. Social smile, B. Can sit without suppo, C. Transfer objects from right to left, D. Can change position from prone to supine
A: Social smile
Answer: A: Social smile 
Explanation: Social smile appears at 3 months