Answer: it is C
The thermistor
Explanation:
 Thermistors (temperature-sensitive, or thermal, resistors) are used as temperature-measuring devices and in electrical circuits to compensate for temperature variations of other components. They are also used to measure radio-frequency power and radiant power, such as infrared and visible light.
To measure the intensity of the electromagnetic wave after knowing the frequency, we can calculate it by using fast fourier transformations (FFT).
