Explanation: Radio waves are electromagnetic waves composed of oscillating electric and magnetic fields, which are always perpendicular to each other and to the direction the wave is traveling. Polarization refers to the orientation of the *electric field* component of this electromagnetic wave. Option C is correct because the polarization of a radio wave is conventionally determined by the direction of its electric field vector. For example, if the electric field oscillates in a vertical plane, the wave is said to be vertically polarized. The phrase "direction of the electromagnetic wave plane" in option C refers to this specific orientation of the electric field. Option D is incorrect because, by definition, polarization is referenced to the electric field, not the magnetic field, even though the two are inextricably linked and perpendicular. Options A and B are incorrect as they describe unrelated phenomena (eddy currents in conductors) or contain inaccurate and poorly defined statements about how electromagnetic waves operate.