This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Fluid and Electrolyte Treatment of Specific Disorders, Subject name: Pediatrics
At what age extracellular fluid is equal to the intercellular fluid? 
Select and explain. 
A. 14 days, B. 4 weeks, C. 2 months, D. 3 months
B: 4 weeks
Answer: B: 4 weeks 
Explanation: b. 4 weeks(Ref: Avery's 8/e p 373)High Yield Points:In fetus & newborn, ECF volume is larger than ICF volume.Normal postnatal diuresis causes an immediate decrease in the ECF volume.This is followed by continued expansion of ICF volume, which results from cellular growth.By 1 year of age, the ratio of the ICF to ECF volume approaches adult levels.