Explanation: A MF/HF Distress priority DSC call is fundamentally designed around the **MMSI (Maritime Mobile Service Identity)**, a unique nine-digit digital identifier for the vessel, which is automatically transmitted with the call. This ensures unambiguous identification in the digital realm, unlike a call sign or vessel name. Crucially, the DSC message must also include the **vessel's position** to enable swift rescue efforts, and the **nature of distress** (e.g., fire, flooding) to inform responders. Following the initial digital DSC alert, further communication about the distress situation transitions to other modes. **J3E (single-sideband voice)** is the primary mode for direct voice communication, while **F1B (radiotelex/Narrow Band Direct Printing - NBDP)** provides a robust, text-based data exchange alternative, particularly useful in challenging radio conditions. Therefore, both J3E and F1B are specified for follow-on communications. Options A is incorrect because follow-on communications are not limited to J3E only. Options C and D are incorrect as the MMSI, not a call sign or vessel name, is the required digital identifier for a DSC call.