Explanation: When the auto-alarm antenna switch is placed in the "auto-alarm operating position," it enables the ship's auto-alarm receiver to actively monitor for distress signals. To ensure the auto-alarm can effectively listen for these critical signals, the ship's own transmitter must be prevented from transmitting. If the transmitter were active, it would generate local interference, making it impossible for the sensitive auto-alarm receiver to detect weak, distant distress calls. Therefore, an automatic safety interlock disconnects the transmitter's keying circuit. This prevents any accidental or intentional transmissions that would deafen the auto-alarm receiver while it is performing its vital listening function. This is a crucial safety measure to maintain the integrity of distress monitoring. Option B is incorrect because if the auto-alarm is off, there's no need to protect it from the ship's transmitter. Option C is incorrect because this specific disconnection is an automatic function tied to the auto-alarm's operation, not solely a manual choice.