This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Medicine
The neonatal kidney achieves concentrating ability equivalent to adult's kidney by: 
Select and explain. 
A. One year of age, B. Eighteen months of age, C. Three to six months of age, D. Just before pubey
A: One year of age
Answer: A: One year of age 
Explanation: Answer is A (One year of age) : "Normal adult kidney can produce urine with an osmolalitv of greater than 1000 m Osm/kg water. The healthy new born infant, subject to water deprivation for 10-14 hours can achieve an osmolality of only 500-700 m osm / kg. This value increases gradually during the first few months and approximates to the adult value by about one year of age."