The correct answer is B. Kilohertz is a unit which measures electromagnetic radio wave frequencies.
A kilohertz (kHz) is a unit of frequency equal to one thousand hertz (Hz). One hertz is equal to one cycle per second. Kilohertz are often used to measure the frequency of electromagnetic waves, such as radio waves. Radio waves are used for a variety of purposes, including communication, navigation, and astronomy.
The other options are incorrect. Power is a measure of the rate at which energy is transferred or converted. Voltage is a measure of the difference in electrical potential between two points. Electric resistance is a measure of the opposition to the flow of electric current.