The correct option is D Amplifier
Amplitude Modulation, AM, is a form of modulation in which the amplitude or intensity of the waveform is varied in line with the waveform of the modulating signal. As part of the modulation process, sidebands are created that extend out either side of the carrier. This is carried out by amplification of wave using amplifier. The audio waveform modifies the amplitude of the carrier wave and determines the envelope of the waveform. In the frequency domain, amplitude modulation produces a signal with power concentrated at the carrier frequency and two adjacent sidebands. Each sideband is equal in bandwidth to that of the modulating signal, and is a mirror image of the other.