Answer:
The answeer is both B and D.
D for sure. Just like how the ground rises over millions of years.
Answer: peptide bonds
Explanation: I think that's the answer.
1. electrical signals travel toward the heart. 2. signal received by the atrioventricular node. 3.signal by the nodes in the atrium. 4.the atria contracts. 5. signal transferred to the ventricles. 6. the ventricles contract.
