A sphere is expanding in such a way that the area of any circular cross section through the sphere's center is increasing at a constant rate of 2 cm²/ sec. At the instant when the radius of the sphere is 4 centimeters, what is the rate of change of the sphere's volume? (The volume V of a sphere with radius r is given by V = 4/3 pi r³.) A B D E 8 cm³/sec 16 cm³/sec 8 cm³/sec 64 cm³/sec 128 cm³/sec​