Answer:
C
Explanation:
If you have more than one variable then you wont know which variable caused the change. Hope this helped, if it did give it a thanks or whatever.
Answer:
Explanation:
1) Excitation brings about contraction.
2) Contraction leads to an increase in blood pressure.
3) Changes in blood pressure results in the opening and closing of the heart valves.
4) The opening and closing of heart valves then regulates the flow of blood and it's volume.
The question is not clear