Final answer:
Hematopoiesis in infants predominantly occurs in the bone marrow, which is the primary site for blood cell formation including the maturation of B cells and the formation of T cells that later mature in the thymus.
Step-by-step explanation:
The process of blood cell formation in infants is known as hematopoiesis. In the early stages of development, including in infants, hematopoiesis takes place in several organs such as the spleen, liver, and lymph nodes. However, as development progresses, the primary site of hematopoiesis becomes the bone marrow. Initially, the yolk sac is involved during embryonic development, which is then succeeded by the aforementioned organs.
Eventually, the red bone marrow of the bones becomes the major site for the generation of blood cells. This includes the differentiation of various cells of the immune system, such as B cells maturing in the bone marrow and T cells maturing in the thymus after their initial formation in the bone marrow. Therefore, the answer to the question 'Where does hematopoiesis occur in infants?' is B) Bone marrow. This includes both the maturation of B cells and the initial formation of T cells, which then migrate to the thymus for further maturation.