Explanation: Connecting the chassis of the Inmarsat terminal to an electrical ground, typically the ship's hull, is crucial for safety. This provides a low-resistance path for any fault current (e.g., if a live wire accidentally touches the metal casing) to flow to ground. This fault current will then trip a circuit breaker or blow a fuse, de-energizing the equipment and preventing the chassis from becoming live, thus eliminating a severe shock hazard. Insulating the DC power supply (A) might prevent electrolysis or ground loops but doesn't directly provide a protective path for fault currents from the terminal's chassis itself. A common busbar (C) aids in proper grounding practices but doesn't "ensure common-mode coupling," which is often an undesirable effect. Isolating the metal frame (D) is extremely dangerous, as it prevents fault currents from clearing, allowing the chassis to become live in the event of an internal fault.