Explanation: An MMSI (Maritime Mobile Service Identity) is a unique, 9-digit number assigned to your vessel and programmed into your Digital Selective Calling (DSC) radio, EPIRB, or AIS transponder. **Why B is correct:** It is crucial to verify that the MMSI programmed into your equipment is correct and matches the number registered to your vessel. If the number is incorrect, your digital distress alerts or routine calls via DSC will transmit the wrong identification, potentially hindering rescue efforts or communication with other vessels. Accessing it helps ensure this vital identifier is accurate. **Why A is incorrect:** While your MMSI identifies you when making a DSC call, you don't "access" your own MMSI *to make a call*. Your radio automatically transmits your pre-programmed MMSI. You would input *another vessel's* MMSI to initiate a call to them. **Why C is incorrect:** Most DSC radios allow the MMSI to be programmed only once by the user. If an MMSI needs to be changed (e.g., after selling the boat or due to a serious error), it often requires a special procedure, such as returning the radio to the manufacturer or a certified dealer for reprogramming, rather than a simple user-accessible change function. **Why D is incorrect:** There are very good reasons to access and verify your MMSI, primarily for accuracy and proper identification in maritime communications and emergencies.