Final answer:
The part of the circulatory system that leads blood back to the heart is the veins. They are designed with valves to prevent backflow and ensure blood's return to the heart for reoxygenation.
Step-by-step explanation:
The part that leads the blood to the heart is b) Veins. Unlike arteries, which take blood away from the heart, veins are the blood vessels specifically responsible for carrying blood back to the heart. This blood is generally deoxygenated after it has circulated through the body and delivered its oxygen to tissues and organs. Veins have valves that help prevent the backflow of blood and maintain its unidirectional flow towards the heart.
When considering the structure and function of blood vessels, an important distinction is that arteries carry blood away from the heart, often rich in oxygen, except for the pulmonary artery. Capillaries are small vessels where the exchange of gases, nutrients, and waste occurs between the blood and tissues. Following this exchange, capillaries lead to venules, which are small veins that merge to form larger veins, eventually carrying the blood back to the heart.