Explanation: Correct grid bias is crucial for audio frequency amplifiers for several reasons. Firstly, **to minimize distortion (A)**, proper bias establishes the tube's DC operating point, ensuring the audio signal remains within the tube's linear operating region. Incorrect bias can cause clipping, compression, or introduce unwanted harmonics, degrading audio fidelity. Secondly, **to set the operating conditions for determining the class of amplification (B)**, the grid bias dictates how much of the input signal cycle results in plate current flow. This defines classes like A, AB, or B, each with different trade-offs between linearity, efficiency, and power output, essential for specific AF amplifier applications. Lastly, **so as not to exceed the rated plate dissipation of the tube (C)**, proper bias prevents excessive plate current flow, especially during idle or signal peaks. Too little negative bias can lead to very high plate current, causing the tube to overheat and potentially fail by exceeding its maximum plate dissipation rating. All these factors are vital for stable, efficient, and high-fidelity AF amplification.