Which of these functions can be performed by a phase-locked loop?

A phase-locked loop (PLL) is a control system that generates an output signal whose phase is related to the phase of an input reference signal. By utilizing a phase detector, a low-pass filter, and a voltage-controlled oscillator (VCO), a PLL can lock onto a reference frequency and generate a wide array of stable, selectable frequencies. This process is known as frequency synthesis. Furthermore, because the control voltage within the loop actively tracks the frequency variations of the incoming signal to maintain the lock, a PLL can inherently be used to demodulate frequency-modulated (FM) signals. The error voltage directly corresponds to the original modulating audio. PLLs are low-level signal processing circuits, so they do not perform tasks like wide-band power amplification or photovoltaic (solar) conversion.