Concept:The pressure of blood on the artery walls is produced mainly by the pumping action of the heart.Explanation:The heart pumps blood by rhythmic contraction and relaxation of its chambers.When the heart contracts, it forces blood into the arteries, causing a rise in pressure.When the heart relaxes, the pressure falls, but it remains higher in arteries than in veins.This cycle of contraction and relaxation is why blood pressure is higher in arteries.Answer:B. contraction and relaxation