Veins are unable to push blood through their vessels by themselves. As such, another method is necessary to help move blood, especially in areas where the blood must move against gravity. What helps move blood through veins?
Group of answer choices
A. Proteins within the veins collect in areas creating a difference in concentration within the blood to allow for diffusion down its concentration gradient
B. The force of the blood moving in the arteries pushes the blood through the veins
C. Veins possess an extra layer of vessel wall which is constantly moving to create wave along the vessel which helps to carry blood through the vessel
D. Contraction of surrounding muscles squeezes veins to push blood through the vessels and valves prevent backflow of the blood