What do veins do in the circulatory system?

Veins play a crucial role in the circulatory system by transporting blood back to the heart. This function is vital for maintaining proper blood circulation throughout the body. After oxygen is delivered to tissues and organs through arteries, the blood, now rich in carbon dioxide and other waste products, returns to the heart through the veins. This process is essential for re-oxygenating the blood in the lungs and ensuring the removal of metabolic waste products from the body's tissues.

The other functions outlined in the other choices do not accurately describe the role of veins. While arteries are responsible for carrying blood away from the heart and distributing oxygenated blood to the body, and while the circulatory system does involve the removal of waste, it is not the veins that are directly responsible for waste removal but rather the overall complexity of blood flow and organ function. Additionally, blood in veins may contain varying levels of oxygen depending on the location in the circulatory system, but veins do not solely transport oxygen; they serve the overall function of returning deoxygenated blood to the heart.