Hematopoiesis first starts in:

ANSWER: (B) Yolk sacREF: 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.