The formula for the volume of a cylinder with a height of 5 units is V(r)=5 pi r^2 where r is the radius of the cylinder. What is the domain and range of this function?

a. r < 0, V(r) < 0
b. r > 0, V(r) < 0
c. r < 0, V(r) > 0
d. r > 0, V(r) > 0