Answer:
The correct answer is D. resting phase
Step-by-step explanation:
Diastole is the resting phase when relaxation of heart muscles takes after contraction(systole). In this phase blood from veins and coronary sinus comes into the auricles and ventricles because of the pressure in the heart is less than veins and opening of A-V valve.
When both auricles and ventricles are relaxed it is called joint diastole. Joint diastole is called complete cardiac diastole and is 0.4 sec long. After the joint diastole auricular systole occurs in which auricles are contracted and ventricles are still relaxed called ventricular diastole.
After the end of auricular systole ventricles contraction starts and auricular relaxation occurs called auricular diastole.