The graph illustrates how the volume of the ventricles changes during the cardiac cycle. At P and R, which valves are open and which are closed?
- Aatrioventricular valve at P closes; semilunar valve at R closes
- Batrioventricular valve at P closes; semilunar valve at R opens
- Catrioventricular valve at P opens; semilunar valve at R closes
- Datrioventricular valve at P opens; semilunar valve at R opens