Final answer:
Correct option (C) In adults, "red bone marrow" is the primary site for the production of red blood cells and the predominant site for white blood cell formation.
Step-by-step explanation:
The primary site of red blood cell production and a major site of white blood cell formation in adults is the red bone marrow. This tissue is responsible for hematopoiesis, the process where blood cells, including erythrocytes (red blood cells), leukocytes (white blood cells), and platelets, are produced. During embryonic development, other organs such as the liver and spleen also play a role in hematopoiesis, but as an adult, the red bone marrow becomes the main site. Moreover, although the B cells mostly develop in the red bone marrow, T cells after initially arising from the red bone marrow migrate to the thymus to mature.