Explanation: Bypass capacitors connected across the brushes of a high-voltage DC generator serve a dual purpose. Firstly, as brushes move across the commutator segments, microscopic arcing occurs. This arcing generates broadband Radio Frequency (RF) noise, which can interfere with radio communications and other sensitive electronics. A bypass capacitor provides a low-impedance path for these high-frequency noise currents, shunting them away from the generator's output lines and effectively reducing the RF interference. Secondly, these same arcing and switching actions can create rapid voltage transients or surges. By providing a path for these sudden changes in current, the capacitors help to absorb and attenuate these high-voltage spikes, thereby offering a degree of protection to the generator windings and connected circuitry from such surges. Option A is incorrect because while capacitors smooth out ripple, they do not actively regulate voltage in the way a voltage regulator circuit does. Therefore, option D encompasses both critical functions.