Final answer:
The largest white blood cell that can leave the bloodstream and transform into a macrophage is the monocyte, which is also involved in phagocytosis and inflammation.
Step-by-step explanation:
The white blood cell that is largest in size and can leave the bloodstream to enter the tissues as a macrophage is the monocyte (Answer: C). Monocytes circulate in the blood and lymph systems and differentiate into macrophages once they move into infected tissue. They are crucial to the body's immune response, with the ability to phagocytize (engulf and digest) debris, foreign pathogens, and other damaged cells. Additionally, macrophages release chemicals that promote inflammation and help attract other immune cells to the site of infection.