The contraction of the atria (______ ________) is followed by the contraction of the ________ (ventricular systole), and during diastole, all four chambers are _________.
a) Systolic phase, ventricles, relaxed
b) Atrial systole, atria, contracted
c) Atrioventricular contraction, ventricles, expanded
d) Atrial relaxation, atria, contracting