Explanation: A frequency discriminator is a crucial component in an FM (Frequency Modulation) radio receiver. Its primary function is to convert the frequency variations of an incoming FM signal into corresponding amplitude variations (voltage changes). Since the audio information in an FM signal is encoded as changes in frequency, the discriminator effectively "demodulates" the signal, recovering the original audio. * **A) A circuit for detecting FM signals.** This is correct. The discriminator is the core of an FM detector stage, turning frequency shifts into usable audio voltage. * **B) A circuit for filtering two closely adjacent signals.** This describes a highly selective filter, not an FM detector. Filters separate signals by frequency; a discriminator extracts information from a frequency-modulated signal. * **C) An automatic band switching circuit.** This is a control circuit that changes the receiver's operating frequency range, unrelated to signal demodulation. * **D) An FM generator.** An FM generator (modulator) creates FM signals, typically found in a transmitter, which is the opposite function of a discriminator in a receiver.