Answer:
Answer is C.
Explanation:
A. The vessel length is pretty much constant. The body can't length or shorten blood vessels.
B. Blood viscosity is also fairly constant because the composition of blood cannot change quickly enough to change resistance as needed.
C. This is the main way resistance is controlled. The smooth muscle surrounding blood vessels can rapidly respond to hormonal or metabolic stimuli and contract/relax to adjust diameter.
D. Again, temperature is fairly constant in the body and would not be a good way to alter resistance.
The answer is A. The heart pumps blood through the circulatory system, and the lungs help the oxygen transport throughout the respiratory system. :)
The hearts contraction that maintains our blood pressure allowing us to breathe and exchange gases at all levels of respiration, ensuring oxygen is provided to all cells of the body, and waste products are eliminated.
Movement of cell against concentration gradient is called a.osmosis
