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
[{'content': 'Infants acquire adult hemoglobin level at: \nSelect and explain. \nA. Birth, B. End of 1st year, C. Puberty, D. 4 years', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]