The Gradient of a Scalar Field Expressed in Terms $\theta$

The gradient of a scalar field expressed in terms of polar coordinates [r, $\theta$ ] in the plane is (r, $\theta$ ) = + . Use the above result to find a potential function for the conservative vector field (expressed in polar form) F = 3 cos( $\theta$ ) - sin( $\theta$ ) .

A) 4 cos( $\theta$ ) + C
B) - 8r sin( $\theta$ ) + C
C) cos( $\theta$ ) + cos( $\theta$ )
D) cos( $\theta$ ) + C
E) cos( $\theta$ ) + cos( $\theta$ ) + C