Which of the events below does not occur when the semilunar valves are open?
a. ventricles are in diastole.
b. blood enters pulmonary arteries and the aorta.
c. ventricles are in systole.
d. av valves are closed.

Ventricles are in diastole.

Explanation:

Semilunar valves are present at the base of the trunk of aorta and pulmonary artery. Semilunar valves prevent the back flow of blood.

The opening of semi lunar valves causes the closing of atrioventricular valves. Ventricles remains in the systole and blood enters in the pulmonary arteries and aorta. Hence, the ventricles are not in diastole.

Thus, the correct answer is option (a).