This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Cardiovascular system, Subject name: Physiology
[{'content': 'During first, 3-4 month of gestation erythrocytes are formed by \nSelect and explain. \nA. Yolk sac, B. Liver, C. Spleen, D. Bone marrow', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Stages of erythropoiesis according to development areIn the first 2 months of gestation - occurs in yolk sac (Mesoblastic phase)from 3rd month of gestation - In liver and spleen (Hepatic phase)From 20th week of gestation - In red bone marrow (myeloid phaseRef: Medical Physiology Indu Khurana 2015 edition, Page No:104', 'role': 'assistant'}]