What are the basic parts of the circulatory system?

The correct answer identifies the comprehensive components of the circulatory system, which includes the heart, veins, capillaries, arteries, and blood.

The heart is the central organ responsible for pumping blood throughout the body, delivering oxygen and nutrients while removing waste products. Veins and arteries are crucial vessels: veins carry blood back to the heart, while arteries transport oxygen-rich blood away from the heart. Capillaries serve as the small blood vessels where the exchange of oxygen, nutrients, and waste occurs at the cellular level. Blood itself is the fluid that circulates through this network, containing red blood cells, white blood cells, platelets, and plasma, essential for the proper functioning of the circulatory system.

Other options fail to encompass all critical elements of the circulatory system. For example, the mention of airways and lungs in a different option brings in elements used in respiration rather than circulation. Similarly, including kidneys emphasizes their role in filtration and waste regulation, which is outside the primary functions of the circulatory system.