Explanation: Class A amplifiers are characterized by operating in the linear region throughout the entire signal cycle. The active device (transistor or tube) is biased such that it conducts for the full 360 degrees of the input waveform. This ensures the output is a continuous, undistorted representation of the input signal, with the input never reaching the cutoff region. While offering excellent linearity and low distortion, Class A amplifiers are generally the least efficient. In contrast: * **Class B** amplifiers conduct for only 180 degrees (half of the input cycle), entering cutoff for the other half. * **Class C** amplifiers conduct for significantly less than 180 degrees, operating deep into cutoff to achieve high efficiency, typically used with tuned circuits for RF amplification. * **Class D** amplifiers are switching amplifiers that convert the analog input into a series of pulses (e.g., PWM), not a continuous conduction, for very high efficiency.