A Spherical Cell Takes in Nutrients Through Its Cell Wall $\frac{A}{r^{2}}$

Multiple Choice

A spherical cell takes in nutrients through its cell wall at a rate proportional to the area of the cell wall.The rate at which the cell uses nutrients is proportional to its volume.Which of the following expresses the rate at which the cell uses nutrients as a function of its radius, r.(A is a constant.)

A) $\frac{A}{r^{2}}$

B) $\frac{A}{r^{3}}$

C) $A r^{2}$

D) $A r^{3}$