Explanation: Airborne HF (High Frequency) transmitters typically operate at a higher power output, around 100 watts, because HF signals utilize skywave propagation to achieve long-distance communication by reflecting off the ionosphere. This process introduces significant path loss, requiring more power to ensure reliable reception over hundreds or thousands of miles. Conversely, airborne VHF (Very High Frequency) transmitters generally provide a lower RF power output, often around 20 watts. VHF communication relies primarily on line-of-sight propagation. At typical aircraft altitudes, 20 watts is usually sufficient to maintain reliable contact with ground stations and other aircraft within the visual horizon, where greater power offers diminishing returns and is less critical than for skywave. Options A, B, and C either present incorrect power levels or reverse the power requirements relative to their respective frequency bands and propagation characteristics.