During the isovolumetric relaxation phase of the cardiac cycle, the correct answer is that the atrioventricular valves are closed and the aortic and pulmonary valves are also closed. Thus, the correct option is: a) Atrioventricular valves are closed, aortic and pulmonary valves are closed.
In this phase, after the blood has been ejected from the ventricles into the aorta and pulmonary artery, the ventricles begin to relax. The pressure within the ventricles drops, but since the aortic and pulmonary valves are already closed following the ejection of blood, no new blood enters the ventricles. The atrioventricular valves remain closed to prevent backflow of blood from the atria. This state is referred to as ‘isovolumetric’ because the volume of blood in the ventricles does not change, even as the pressure decreases.