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: Physiology
Infants acquire adult hemoglobin level at: 
Select and explain. 
A. Birth, B. End of 1st year, C. Puberty, D. 4 years
B: End of 1st year
Answer: B: End of 1st year 
Explanation: None