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': 'Erythropoiesis in first two months of gestation age takes place in \nSelect and explain. \nA. Yolk sac, B. Placenta, C. Amniotic sac, D. Chorion', 'role': 'user'}, {'content': 'Answer: A \nExplanation: In the first 2 month of gestation. the yolk sac is the main site of blood formation (MESOBLASTIC PHASE) Ref: Medical Physiology Indu Khurana 2015 edition pAge No:104', 'role': 'assistant'}]