Final answer:
The hormone that stimulates erythropoietic activity in the bone marrow is erythropoietin (EPO), which is secreted by the kidneys to promote the production of red blood cells.
Step-by-step explanation:
The hormone that stimulates erythropoietic activity in the bone marrow is d) Erythropoietin. Erythropoietin (EPO) is a glycoprotein hormone that is secreted by the kidneys in response to low oxygen levels in the blood. Its main function is to stimulate the production of red blood cells (erythrocytes) within the bone marrow, which enhances the blood's capacity to transport oxygen throughout the body.
Other options, such as thyroxine, cortisol, and growth hormone, have different functions: Thyroxine (produced by the thyroid gland) regulates metabolism, cortisol (produced by the adrenal glands) is involved in stress response, and growth hormone (produced by the pituitary gland) stimulates growth and cell reproduction. Therefore, these hormones do not have a direct role in stimulating erythropoiesis.