Work Step by Step
Options a. and b. are incorrect. The lungs do not belong to the circulatory system; they belong to the respiratory system, although the lungs do work very closely with the circulatory system. Option d. is incorrect. Although the items given are all correct, one important ingredient is missing: blood. Blood is an essential part of the circulatory system. Option c. is correct. The heart pumps blood through a series of blood vessels to nourish the tissues of the body. Therefore, the parts of the circulatory system are the heart, the blood vessels, and blood.