Vein is a blood vessel that exhibit thin muscular walls and it brings the deoxygenated blood from all the cells, tissues and organs back to the heart. In the veins the valves are present which prevent the backward flow of blood. Lumen of the vein is wide.
According to the above information vein is the correct option.
The right answer is vein (it contains blood and has valves).
The infra-cardiac veins of small and medium caliber possess this system of fight against gravity. The valves consist of a dense connective tissue, surmounted by endothelial cells, corresponding to a fold of the intima. They allow blood circulation in the sense organ / heart but prevent venous reflux.
The tilt of the earth during its revolution around the sun causes the north pole to point away from the sun more than at any other time, thereby receiving no sunlight.
The age structure of a population is the distribution of people of various ages. It is a useful tool for social scientists, public health and health care experts, policy analysts, and policy-makers because it illustrates population trends like rates of births and deaths.
