This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: All India exam, Subject name: Physiology
[{'content': 'First change of improvement, noted after iron therapy is initiated \nSelect and explain. \nA. Decreased irritability, B. Reticulocytosis, C. Increase in serum iron levels, D. Replenishment of iron stores', 'role': 'user'}, {'content': 'Answer: A \nExplanation: 12-24 hr Replacement of intracellular iron enzymes; subjective improvement; decreased irritability; increased Appetite 36-48 hr Initial bone marrow response; erythroid hyperplasia 48-72 hr Reticulocytosis, peaking at 5-7 days 4-30 days Increase in hemoglobin level 1-3 mo Repletion of stores', 'role': 'assistant'}]