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
Brain size achieves 90 % of adult size by the age of: 
Select and explain. 
A. 2 years, B. 4 years, C. 6 years, D. Puberty
A: 2 years
Answer: A: 2 years 
Explanation: Ans: aRef: Still searching