Explanation: The auto-alarm signal, also known as the radiotelegraph alarm signal, consists of two distinct audio tones transmitted alternately. Specifically, it involves a 2200 Hz tone and a 1300 Hz tone. Each tone has a duration of 250 milliseconds (0.25 seconds). The critical characteristic that makes "A) 0 seconds" correct is that these two tones are transmitted *alternately without interruption*. This means there is **0 seconds** of silence or space between the end of one tone (e.g., 2200 Hz) and the beginning of the next tone (1300 Hz). The transition between the alternating tones is immediate and continuous for the entire duration of the alarm signal (typically 30 to 60 seconds). Options B and C are incorrect because they describe different patterns and durations that do not correspond to the internationally defined radiotelegraph alarm signal. The signal is not composed of dashes of 5-3.5 seconds or a series of five specific dashes, nor does it have variable spaces between elements in the manner described.