1. During the atrial systole, the atrial muscles _______.   relax   contract   2. The cardiac veins carry blood to the walls of the heart.   True   False   3. When the auricles of the heart contract, the ventricles relax, and vice versa.   True   False   4. Plasma is a constituent of blood.   True   False   5. During the ventricular systole, the blood enters the ventricles.   True   False   6. During the ventricular systole, the semilunar valves are closed.   True   False   7. In a normal adult, the red blood corpuscles are produced in the liver.   True   False