This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Anaemia in Pregnancy, Subject name: Gynaecology & Obstetrics
[{'content': 'Initial site of RBC production in fetus \nSelect and explain. \nA. Gestational sac, B. Yolk sac, C. Placenta, D. Fetal bones', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Hematopoiesis - 1st demonstrable in yolk sac followed by liver and then finally spleen and bone marrow life span of fetal RBCs at term - 90 days', 'role': 'assistant'}]