The electric field in a region around the origin is given by Vector E = C(xˆi + yˆj), where C is a constant. The equipotential surfaces in that region are:
A. concentric cylinders with axes along the z axis
B. concentric cylinders with axes along the x axis
C. concentric spheres centered at the origin
D. planes parallel to the xy plane
E. planes parallel to the yz plane
