Final answer:
The period when the semilunar valves are open and blood flows out of the ventricles is during ventricular systole, which corresponds to option 1) Systole.
Step-by-step explanation:
The period of time when the semilunar valves are open and blood flows out of the ventricles is known as ventricular systole. During this phase, after the atria relax (atrial diastole), the ventricles contract, pushing blood out of the heart through the pulmonary valve to the lungs and through the aortic valve to the rest of the body. The opening of the semilunar valves occurs as the ventricular pressure exceeds the pressure in the aorta and the pulmonary arteries, allowing for the ejection of blood. Hence, the correct answer is 1) Systole.