Final answer:
The correct answer is d. myostatin, which is a protein that negatively regulates cell growth, particularly in muscle cells.
Step-by-step explanation:
In the context of cell signaling and the regulation of cell behaviors such as survival, growth, and proliferation, some proteins serve to stimulate these processes while others inhibit them. Among the options provided, myostatin is a protein that acts negatively on other cells, inhibiting their growth and proliferation. Myostatin is known for its role in regulating and limiting muscle growth; thus, the correct answer is d. myostatin. In contrast, TNF-alpha is involved in inflammation and cell death, Wnt is associated with cell signaling in development, and EGF is a growth factor that stimulates cell growth and division.