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6. The heart has two pumps. Each pump has two chambers, the upper and lower chambers. There is a valve between each atrium and ventricle. In what ways are valves important in the circulation of blood? I Valves control muscle contractions of the heart. II. Valves control movement of blood into the heart chambers and out to the aorta and the pulmonary artery. III. Valves keep the blood moving in only one direction A. I and II only B. I and III only C. II and III only D. I, II and III​