Pacemaker is the correct answer
Answer:
All of the above.
Explanation:
There isn't a need for this, it just is.
Answer:With this system, blood always flows in only one direction inside the heart. There are also valves at the bottom of the large arteries that carry blood away from the heart: the aorta and the pulmonary artery. These valves keep the blood from flowing backward into the heart once it has been pumped out.
Explanation:
Which one of the following choices best represents a symptom of overtraining?
b. irritability