Explanation: A properly operated Class A audio amplifier is designed for high fidelity and linearity. It biases the active device (transistor or tube) to conduct current for the entire 360 degrees of the input signal's cycle. This ensures that the output waveform is a faithful, scaled reproduction of the input, meaning it introduces very little distortion and thus produces no serious modification of the input waveform. Option B is incorrect because serious distortion is the opposite of what a properly operated Class A amplifier achieves. Distorted output would indicate improper operation, such as overdriving the amplifier or incorrect biasing. Since Class A aims for linearity, options C and D, which include "serious distortion," are also incorrect.