Which of the following can be used to generate FM phone signals?

Frequency Modulation (FM) is created by directly varying the frequency of an oscillator in step with an audio signal. A reactance modulator achieves this by using a device, such as a varactor diode, whose capacitance changes with the applied audio voltage. When placed in the frequency-determining circuit of a local oscillator, it shifts the oscillator's frequency up and down, producing an FM signal. Balanced modulators are used to generate Double Sideband Suppressed Carrier (DSB-SC) signals, which are a primary step in generating Single Sideband (SSB), not FM. Therefore, any option mentioning balanced modulation is incorrect for generating FM. Furthermore, you must modulate an oscillator to create true FM, not a final amplifier. Modulating the final amplifier changes the amplitude of the output, which generates Amplitude Modulation (AM), not FM.