The region R is bounded by the y-axis, y = 4 and y = x^2. Which of these expressions represents the volume of the solid formed by revolving R about the x-axis?

a. [tex] \int\limits^2_0 { \pi (16-x^4)} \, dx [/tex]
b. [tex] \int\limits^2_0 { \pi (4 - x^2)^2} \, dx [/tex]
c. [tex] \int\limits^2_0 { \pi (16-x^4)^2} \, dx [/tex]
d.[tex] \int\limits^2_0 {2\pi x(4 - x^2)} \, dx [/tex]
e. None of the above