(a) Describe the set of points whose distance from the z-axis equals the distance from the xy-plane.

A. A cylinder opening along the y-axis
B. A cone opening along the x-axis
C. A cone opening along the y-axis
D. A cylinder opening along the x-axis
E. A cylinder opening along the z-axis
F. A cone opening along the z-axis

(b) Find the equation for the set of points whose distance from the z-axis equals the distance from the xy-plane.

A. $y^2 = x^2 + z^2$
B. $y^2 + z^2 = r^2$
C. $x^2 + y^2 = r^2$
D. $z^2 = x^2 + y^2$
E. $x^2 + z^2 = r^2$
F. $x^2 = y^2 + z^2$