Explanation: In a Class B amplifier, the active device (tube in this case) is biased at or very near cutoff. This means that plate current flows for approximately one-half, or 180 degrees, of the input excitation voltage cycle. Option A, "Slightly more than 180 degrees," is correct because practical Class B amplifiers, especially in push-pull configurations, are often biased *just above* cutoff. This slight offset prevents "crossover distortion" – a noticeable distortion that occurs when the current from one half of the amplifier circuit turns off before the other half fully turns on. By allowing a small overlap, conduction occurs for a few degrees more than 180, ensuring a smoother transition and cleaner output signal. Option B, "Slightly less than 180 degrees," would typically result in severe crossover distortion and is characteristic of Class C operation if significantly less. Option C, "360 degrees," describes Class A amplifier operation, where the tube conducts for the entire input cycle.