Explanation: Parasitic oscillations in a power amplifier are unwanted self-oscillations at frequencies other than the intended operating frequency, often due to inherent capacitance within the active devices (like transistors or vacuum tubes). This internal capacitance can provide a feedback path from the output back to the input, creating an oscillator rather than a stable amplifier. **C) By neutralization.** Neutralization is the direct method to combat this. It involves introducing an intentional feedback path, equal in magnitude but opposite in phase to the internal undesired feedback capacitance. This effectively cancels out the internal feedback, preventing the amplifier from oscillating parasitically and ensuring stable operation only at the desired frequency. **A) By tuning for maximum SWR** is incorrect. Maximum SWR indicates a severe mismatch, causing most power to reflect back to the amplifier. This is detrimental to efficiency and can damage the amplifier, and does not address the cause of parasitic oscillations. **B) By tuning for maximum power output** and **D) By tuning the output** are related to optimizing the amplifier's performance at the desired frequency. While proper tuning is important for efficiency and desired signal transfer, it does not inherently eliminate parasitic oscillations, which originate from internal feedback mechanisms. An amplifier can still experience parasitic oscillations even when tuned for maximum power output at the intended frequency.