Explanation: A buffer amplifier stage in a transmitter is primarily used to isolate the oscillator from subsequent stages, such as power amplifiers or mixers. Oscillators are very sensitive to changes in the electrical load connected to them, which can cause their output frequency to drift, a phenomenon called "frequency pulling." The buffer amplifier has a high input impedance and a stable output impedance, presenting a constant load to the oscillator. This isolation prevents impedance variations in the following stages from affecting the oscillator's delicate resonant circuit. By doing so, the buffer amplifier ensures that the oscillator maintains a very stable output frequency, which is crucial for precise and reliable radio communication. Option A describes functions related to FM demodulation or frequency control, not the primary role of a buffer in a transmitter's oscillator stage. Option B is vague and does not accurately describe the buffer's function; its role is isolation and impedance matching, not "buffering signals imposed upon the carrier" in a correctional sense. Therefore, improving the frequency stability of the oscillator (C) is the correct and most important function.