(N/A) $(1)$ Deoxygenated (impure) blood enters the right ventricle from the right atrium. This blood must be sent to the lungs via the pulmonary arteries for oxygenation. In the lungs,the blood releases $CO_{2}$ and absorbs $O_{2}$,becoming oxygenated (pure) before returning to the left atrium.
$(2)$ The heart is called a double pump because it performs two distinct pumping actions in one complete cardiac cycle. The right side of the heart pumps deoxygenated blood to the lungs for oxygenation (pulmonary circulation),while the left side of the heart pumps oxygenated blood to the rest of the body (systemic circulation). This separation ensures efficient transport of gases.