D. Size of the oxygen atom compared to the hydrogen atom
C. Ball and socket joints
Just took the test hope this helps :)
I believe, for the artery, they have, an open, circular lumen an a thick media
Veins on the other hand, have somewhat collapsed lumen and a thinner media. Arteries are blood vessels that carry blood out of the heart to other parts of the body, all arteries carry oxygenated blood except the pulmonary artery which carries deoxygenated blood from the heart to the lungs. Veins carry blood from other body parts to the heart, all veins carry deoxygenated blood except the pulmonary vein which caries oxygenated blood from the lungs to the heart.
Answer:
Natural selection. It is simply the process by which random variations that give an individual a favorable adaptation to its environment survive to be passed on to offspring.