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
Predominant site of erythropoiesis during 6th month of gestation is? 
Select and explain. 
A. Yolk sac, B. Liver, C. Bone marrow, D. Thymus
B: Liver
Answer: B: Liver 
Explanation: ANSWER: (B) LiverREF: Guyton, 6th edition, page 420Production of Red Blood Cells: In the early weeks of embryonic life, primitive, nucleated red blood cells are produced in the yolk sac. During the middle trimester of gestation, the liver is the main organ for production of red blood cells, but reasonable numbers are also produced in the spleen and lymph nodes. Then, during the last month or so of gestation and after birth, red blood cells are produced exclusively in the bone marrow.