Explanation: An "AGC" button activates the Automatic Gain Control circuit within a receiver. The fundamental purpose of AGC is to maintain a relatively consistent audio frequency (AF) output level despite fluctuations in the strength of the received radio signal. When the input signal to the receiver varies (e.g., due to fading, antenna movement, or changes in the distant transmitter's power), the AGC circuit automatically adjusts the gain of the receiver's radio frequency (RF) and intermediate frequency (IF) amplifier stages. If the incoming signal strengthens, the AGC *reduces* the amplifier gain to prevent the audio from becoming excessively loud. Conversely, if the signal weakens, the AGC *increases* the gain to prevent the audio from fading into the noise. This continuous, automatic adjustment ensures a stable and comfortable listening experience, making option A correct. Options B and C describe actions opposite to the AGC's function. Option B is incorrect because AGC increases gain for weak signals. Option C is incorrect as AGC reduces gain for strong signals. Option D is incorrect as AGC affects receiver output, not transmitter RF output.