This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Physiology
Erythropoiesis in early fetal life occurs in 
Select and explain. 
A. Yolk sac, B. Vertebrae, C. Bone marrow, D. Spleen
A: Yolk sac
Answer: A: Yolk sac 
Explanation: None