Explanation: Class C amplifiers are characterized by operating the vacuum tube with a bias such that plate current flows for significantly less than 180 degrees of the input signal cycle, typically between 90 and 150 degrees. This "burst" mode of operation means the tube is only active for a short period during each cycle, resulting in very high plate circuit efficiency, often 70-85% or even higher. Because the current is drawn in short bursts, the individual output waveform from the tube is highly distorted. However, Class C amplifiers are primarily used in RF applications for amplifying unmodulated carrier waves or FM signals, where the output is fed into a high-Q resonant tank circuit. This tank circuit "rings" or stores energy, smoothing out the distorted pulses from the tube and reconstructing a clean sinusoidal output at the resonant frequency. Option A describes characteristics closer to a Class A amplifier (low efficiency, 360-degree conduction, low distortion). Option B describes characteristics of Class B or AB amplifiers (medium efficiency, conduction around 180 degrees). Therefore, option C accurately describes the high efficiency, burst-like current flow, and inherent distortion of a vacuum tube operating in Class C.