Explanation: A DSC Distress Relay is a crucial element of the Global Maritime Distress and Safety System (GMDSS). Its purpose is to ensure that a distress alert, initially sent by a vessel in peril, is ultimately received by search and rescue authorities. Option A correctly identifies this circumstance: if a vessel (or a coast station) receives a DSC Distress alert but observes no subsequent acknowledgment from a competent shore station or another ship designated to handle it, the Master of the receiving vessel must decide if a relay is necessary. This action ensures the distress situation does not go unnoticed, prompting the initiation of rescue efforts. Option B is incorrect; while knowing the MMSI is helpful, the inability to determine it does not negate the need for a relay if the distress alert remains unacknowledged. Option C is incorrect because a relay is generally made *if there is no acknowledgment*, not after one. An acknowledgment means the alert has been received. Option D is incorrect; a relay's purpose is to ensure the alert reaches authorities, regardless of the relaying vessel's proximity or ability to assist directly.