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': 'Brain size achieves 90 % of adult size by the age of: \nSelect and explain. \nA. 2 years, B. 4 years, C. 6 years, D. Puberty', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans: aRef: Still searching', 'role': 'assistant'}]