Explanation: After a distress call has been transmitted, all subsequent transmissions relating to that distress, including distress-traffic radiotelegrams, must be clearly identified. The correct procedure, as outlined in international radio regulations and FCC rules, is to precede the preamble of every distress-traffic radiotelegram with the appropriate distress signal. For radiotelephony (voice), this is "MAYDAY"; for radiotelegraphy (Morse code), it is "SOS." This distress signal is then followed by the call sign of the station transmitting the message. This ensures that any station monitoring the frequency immediately recognizes the extreme urgency and nature of the communication, granting it absolute priority. Therefore, option B is correct because it accurately describes this requirement: "The distress signal preceding the call and repeated at the beginning of the preamble." Option A is incorrect because "SOS" is specific to radiotelegraphy; the general term "the distress signal" (as in option B) covers both "MAYDAY" and "SOS," making it more comprehensive and accurate for all modes of transmission. The critical element is the distress signal itself, regardless of whether it's MAYDAY or SOS, prominently placed in the preamble.