when working out you want to make sure you can meet the task at hand. go little by little until you are able to meet your goal. so to start i would rule out D.
They are usually between the ages of teenage and adulthood
Answer:
your answer would be sinus node (also called the sinoatrial node, or SA node).
Explanation:
Experts in trauma and emergency care center call the first hour after serious injury as the most critical in determining chances for survival
