Answer: circulatory system
Explanation:
Blood that return from the upper and lower parts of the body are deoxygenated hence they are transported to the heart for oxygenation. therefore blood enter the heart through vena cava ( the main vein) to the right auricles and it goes to the lower part of the heart which is the right ventricles which is more muscular. due to this blood is pumped from the right ventricles through pulmonary vein which pumps blood to the left ventricles through pulmonary artery and it is allowed to the left ventricles in the lower part of the heart and it pumped back in the body through the aorta( the main artery) .
