What do veins primarily carry?

Veins primarily carry deoxygenated blood back to the heart, which contains carbon dioxide and waste products that need to be removed from the body. This is essential for maintaining proper circulatory function and ensuring that the blood can be reoxygenated in the lungs before being pumped out again to supply the body's tissues.

The other choices, while they play important roles in the circulatory system, do not reflect the primary function associated with veins. For example, oxygen-rich blood is carried by arteries, which transport it away from the heart to various parts of the body. Nutrients are absorbed by the bloodstream primarily through the digestive system and are also typically carried by arteries. Hormones, although they can be present in the bloodstream, do not specifically characterize the primary function of veins either, as they are circulated throughout the body via different pathways suited for hormonal transport. Thus, the primary role of veins is indeed to transport waste products along with deoxygenated blood back to the heart.