Which of the following affects blood volume?

Select one:

a. The speed at which the blood flows

b. The strength at which the heart contracts

c. The amount of water present in the blood

d. The rate at which the heart contracts

I think that it is D. D because the rate that your heart contracts is how much it is pumping. If you have adrenaline pumping through you, your heart is contracting faster and your blood is thicker by it. But when you calm down your blood goes back to normal.