When Changing from Cartesian to Spherical Coordinates $\frac { \partial r } { \partial z } =$

Multiple Choice

When changing from Cartesian to spherical coordinates, $\frac { \partial r } { \partial z } =$

A) $\cos \phi$
B) $\cos \theta$
C) $\tan \theta$
D) $\sin \phi$
E) $\sin \theta$