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
[{'content': 'A 3 month baby can do: \nSelect and explain. \nA. Social smile, B. Can sit without suppo, C. Transfer objects from right to left, D. Can change position from prone to supine', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Social smile appears at 3 months', 'role': 'assistant'}]