This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Heart, Circulation, and Blood, Subject name: Physiology
[{'content': 'In erythropoiesis: \nSelect and explain. \nA. Size of the cells increases in subsequent stages, B. Haemoglobin appears at early normoblast stage, C. Mitosis occurs in the late normoblast at the fastest rate, D. Folic acid is useful as a maturation factor', 'role': 'user'}, {'content': 'Answer: D \nExplanation: D', 'role': 'assistant'}]