What are the main structures of the cardiovascular system?

The main structures of the cardiovascular system include capillaries, arteries, veins, and the heart, which work together to circulate blood throughout the body.

Capillaries are the smallest blood vessels where the exchange of oxygen, carbon dioxide, nutrients, and waste occurs between blood and tissues. Arteries carry oxygen-rich blood away from the heart to the body's tissues under high pressure. Veins return oxygen-poor blood back to the heart at lower pressure. The heart acts as the central pump of the cardiovascular system, continuously pushing blood through this network of vessels.

This combination of arteries, capillaries, veins, and the heart creates an efficient system for transporting blood, which is essential for sustaining bodily functions. The other options include structures not primarily involved in the cardiovascular system or misrepresent the essential components, demonstrating that choice B is indeed the most accurate representation of the main structures involved.