Final answer:
The heart beats in a specific sequence: both atria beat simultaneously, followed by both ventricles beating simultaneously.
Step-by-step explanation:
The heart beats in a specific sequence to efficiently pump blood throughout the body. The correct answer is D. Both atria beat simultaneously, followed by both ventricles beating simultaneously. In this sequence, the electrical impulses in the heart cause the atria to contract at the same time, pushing blood into the ventricles. Then, the ventricles contract together, pumping blood out of the heart to the lungs or the rest of the body.