This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Blood: RBCs, Anemia, and Polycythemia, Subject name: Physiology
[{'content': 'Up to 6 weeks of gestation erythropoiesis occurs in? \nSelect and explain. \nA. Yolk sac, B. Bone marrow, C. Spleen, D. Liver', 'role': 'user'}, {'content': "Answer: A \nExplanation: ANSWER: (A) Yolk sacREF: Guyton, 6th edition, page 420, Wintrobe s clinical hematology 12th ed page 90, William's hematology 8th ed chapter 6See details of fetal erythropoiesis in Physiology December 2011", 'role': 'assistant'}]