Function of semilunar valves in the heart​

They close to prevent blood from flowing back into the ventricles.

Explanation: To find the semilunar valve is the valve between the left ventricle and the aorta is the aortic semilunar valve.

i have to report this, it doesn't relate to biology

hydrogen is a compound or a single element and a element is a pure substence that cannot be separated into simpler subtances

clorine is a compound its a chemical substance that forms when two or more different elements combine

so both hydrogen and clorine are compounds