Name the three phases of hematopoiesis.

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Hematopoiesis develops in three sequential sites during embryogenesis. The earliest wave is primitive erythropoiesis in the yolk sac, often called the mesoblastic or primitive phase, which produces the first red cells. Next, definitive hematopoiesis arises in the fetal liver (hepatic phase), with development of multiple blood lineages. Finally, hematopoiesis shifts to the bone marrow (medullary or myeloid phase), becoming the lifelong site of blood cell production. The thymus is a maturation site for T cells, not a primary hematopoietic site, which is why that option isn’t fitting. Also, the term “megaloblastic” here isn’t a phase of hematopoiesis. So the correct trio is primitive/mesoblastic in the yolk sac, hepatic phase in the liver, and medullary/myeloid phase in the bone marrow.