Which message categories cannot be disabled by the GMDSS Radio Operator?

Correct Answer: Option D — All of the above

Under IMO and GMDSS carriage requirements, specific safety-critical information, including Search and Rescue, navigational, and meteorological warnings, must be received by all vessels. These categories are hard-coded into the equipment to ensure that vital safety data cannot be suppressed by the operator, maintaining situational awareness for all mariners.