This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Body composition and Acid base Balance, Subject name: Pediatrics
At what age the ratio of the ICF to ECF volume approaches adult levels? 
Select and explain. 
A. 14 days, B. 4 weeks, C. 6 months, D. 1 year
D: 1 year
Answer: D: 1 year 
Explanation: By 1 year of age, the ratio of the ICF to ECF volume approaches adult levels.