This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Fluid and electrolytes, Subject name: Pediatrics
The ratio of ICF volume to Extracellular fluid volume reaches adult values at the age of 
Select and explain. 
A. 1 year, B. 2 years, C. 3 years, D. 4 years
A: 1 year
Answer: A: 1 year 
Explanation: Total body water is divided between 2 main compaments: intracellular fluid (ICF) and extracellular fluid (ECF). In the fetus and newborn, the ECF volume is larger than the ICF volume. The normal postnatal diuresis causes an immediate decrease in the ECF volume. This is followed by continued expansion of the ICF volume, which results from cellular growth. By 1year of age, the ratio of the ICF volume to the ECF volume approaches adult levels.Reference: Nelson Textbook of Paediatrics; 20th edition; Chapter 55; Electrolyte and Acid-Base Disorders