Explanation: Passenger ships equipped with a GMDSS (Global Maritime Distress and Safety System) installation are subject to specific international and national regulations concerning maritime safety. These regulations mandate that at least two operators on board hold a GMDSS-specific license. The type of license required—either a GMDSS Radio Operator License or a Restricted GMDSS Radio Operator License—depends on the vessel's operating areas (Sea Areas A1, A2, A3, or A4), ensuring proper operation of all GMDSS functions and continuous watchkeeping. Licenses such as the General Radiotelephone Operator License (A), Restricted Radiotelephone Operator Permit (B), or Marine Radio Operator Permit (C) are generally not sufficient for the primary operational requirements of a GMDSS-equipped passenger ship. While a General Radiotelephone Operator License is a high-level certification, it doesn't specifically cover the operational watchkeeping requirements for GMDSS. Options B and C are typically for less complex operations or vessels not subject to compulsory GMDSS carriage requirements.