Answer:
b. The ventricles are in diastole.
Explanation:
Atrial systole is the phase of the cardiac cycle that lasts for about 0.1 sec. During this phase, the atria are contracting. At the same time, the ventricles are relaxed or are in diastole. The pressure of the contraction of atria forces the blood to open the AV valves. The blood enters the ventricles through the open AV valves. During this phase, the semilunar valves are closed as the blood pressure in ventricles is very low. The P wave of ECG represents the atrial systole. This is followed by the systole of ventricles.
