The right option is; A. Veins
Veins are the blood vessels that have thin walls and contain valves.
Veins are blood vessels, and an essential part of the circulatory system that mainly functions by transporting deoxygenated blood back to the heart after arteries transports blood out. Most veins have valves in them to avoid backflow, and their walls are very thinner than that of arteries. The biggest vein in the body is the vena cava. Veins are grouped into; systemic veins, superficial veins, deep veins, pulmonary veins, and communicating veins.