Final answer:
Capillary beds have the highest total cross-sectional area in the systemic vascular system due to the vast number of capillaries, despite each having a small diameter.
Step-by-step explanation:
The vessels in the systemic vascular system with the highest total cross-sectional area are the capillary beds (b). Although each capillary has a very small diameter, the vast number of capillaries across the body significantly increases the total cross-sectional area available for blood flow. In contrast, arteries and arterioles have thicker walls and are under higher pressure, whereas veins have a larger diameter but fewer in number leading to a smaller cross-sectional area. While arterioles have smaller lumens and contribute to higher resistance in blood flow, it is the capillaries that have the greatest total cross-sectional area.