Which statement accurately describes veins?

Veins are blood vessels that are primarily responsible for returning deoxygenated blood to the heart, with the exception of the pulmonary veins, which carry oxygenated blood from the lungs back to the heart. This return is essential for the circulatory system to function effectively, as it ensures that blood can be re-oxygenated in the lungs and then pumped back out to the body. Veins have thinner walls compared to arteries and often include valves that prevent the backflow of blood, aiding in the return process against the force of gravity, especially in the limbs. The structure and function of veins are crucial for maintaining blood circulation, making the statement that they carry blood back to the heart accurate and fundamental in understanding the vascular system.