Ralph is looking at a blood vessel under a microscope as part of his study about the cardiovascular system. he notices that the vessel contains blood and has valves. what is the blood vessel that he is observing?
a. capillary
b. vein
c. lymph
d. artery

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.

b. vein

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.

it's diluted or concentrated

in a diluted solution, you can add a lot more solute but in concentrated only a little more can be added