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: Pediatrics
Which of the following is the predominant site of erythropoiesis during 7 month of gestation? 
Select and explain. 
A. Yolk sac, B. Liver, C. BM, D. Thymus
B: Liver
Answer: B: Liver 
Explanation: In the human, large nucleated blood cells are first formed in the yolk sac and some enucleate. During the second gestational month, erythropoiesis moves to fetal liver, wherein smaller, but still macrocytic, non nucleated cells are produced. At bih, the hepatic phase of blood cell production ceases, and erythropoiesis moves to the marrow. Ref: Prchal J.T. (2010). Chapter 31. Production of Erythrocytes. In J.T. Prchal, K. Kaushansky, M.A. Lichtman, T.J. Kipps, U. Seligsohn (Eds), Williams Hematology, 8e.