Explanation: When a Digital Selective Calling (DSC) message is received, the equipment uses an Error Checking Code (ECC) to verify the integrity of the transmitted data. If the ECC is "no good," it means the received data is corrupted or contains errors, rendering the specific details of the message unreliable. Here's why option A is correct: * **Some portion of the call particulars will appear on the screen:** Even with a bad ECC, the receiving equipment might be able to decode enough information (like the calling station's MMSI or the type of call) to indicate that a call was received, alerting the watch officer. * **The channel will not change:** The GMDSS system is designed for reliability and safety. If the ECC fails, the proposed working frequency requested in the routine call cannot be reliably determined. Consequently, the DSC controller will not automatically switch to a potentially incorrect or unknown channel based on corrupted data. This prevents the vessel from inadvertently moving off its watchkeeping frequency or switching to an inappropriate channel. Here's why the other options are incorrect: * **B) The ECC alarm will sound and the watch officer should call back to determine the working frequency:** While an alarm is plausible, and the watch officer might need to call back, the question asks about *automatic actions*. The equipment will not automatically facilitate a call-back in this scenario, and the core issue is the immediate equipment response to corrupted data. * **C) The ECC alarm will sound and the channel will change but the watch officer should ensure it is legal:** The channel will *not* automatically change if the working frequency information is corrupted by a bad ECC. Changing channels based on unreliable data would be unsafe and goes against GMDSS operational principles. * **D) The channel will not change because the working frequency requested is illegal:** While the channel will not change (matching option A), the reason is the *data corruption* (bad ECC), not necessarily that the *intended* working frequency was illegal. The equipment cannot even reliably determine if the requested frequency is legal if the data describing it is corrupt.