Express the surface $$x = 3\cos\theta \sin\phi, y = 4\sin\theta \sin\phi, z = 6\cos\phi$$ as a level surface $f(x,y,z) = 5184$,
$f(x,y,z) =$

This surface is a

A. ellipsoid
B. hyperboloid
C. paraboloid
D. sphere
E. None of these