Why Do Veins Have Relatively Thin Walls

Why do veins have relatively thin walls?

A) It allows a typical vein to change the diameter of its lumen.
B) It allows a typical vein to be stretched as its diameter increases during ventricular systole.
C) A typical vein's wall allows exchange to occur quickly by diffusion across endothelial cells or through gaps between adjacent endothelial cells.
D) A typical vein does not need to withstand much pressure.
E) There are sphincters associated with the walls of veins, which allow vasomotion to occur.