Consider the blood vessels pictured below. Which statement best explains this type of blood vessel and the function of these vessels’ valves?

A. These are arteries, which prevent the backflow of blood because the walls have little muscle to pump blood back to the heart.
B. These are veins, which prevent the backflow of blood because the walls have little muscle to pump blood back to the heart.
C. These are arteries, which prevent the backflow of blood because the walls have little muscle to pump blood into the capillaries.
D. These are veins, which prevent the backflow of blood because the walls have little muscle to pump blood into the capillaries.