The correct answer is D: All these choices are correct. There are separate electric (E) and magnetic (H) MPE limits at frequencies below 300 MHz because the body reacts to both E and H fields, ground reflections cause field strength to vary, and E and H field peaks can occur at different locations. All these factors require separate limits. At frequencies below 300 MHz, the wavelength is long compared to typical distances, so E and H fields don't have a fixed relationship (unlike far-field where E and H are proportional). The body can react differently to E and H fields. Ground reflections and scattering cause field strength to vary significantly with location. E field and H field intensity peaks can occur at different places. Therefore, separate E and H field limits are needed to properly protect against exposure. Above 300 MHz, E and H are proportional in the far field, so a single power density limit is sufficient.