Your answer would be C. I got that because “At the same time that the left ventricle pumps blood into the aorta, the right ventricle Carrie’s blood into the pulmonary artery. The pulmonary Artery carries blood to the lungs to attain oxygen and discard carbon dioxide. Once these gases are traded, the blood returns to the heart through a system of veins that lead to the main pulmonary vein. The pulmonary vein dumps the oxygen-rich blood into the left atrium. When the valve opens between the left atrium and left ventricle, the blood fills the ventricle and the cycle continues.” Meaning the C would be the answer of it is a part of the circulatory system.