This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Growth, Development, and Behavior, Subject name: Pediatrics
[{'content': 'A child can wave "bye-bye" by what age: \nSelect and explain. \nA. 6 months, B. 9 months, C. 12 months, D. 18 months', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Ans. B. 9 monthsKey social and adaptive milestones2 months Social smile3 months Recognizes mother6 months:- Recognizes strangers9 months:- Waves "bye-bye"', 'role': 'assistant'}]