Explanation: The frequencies listed in option C are designated international maritime working frequencies for follow-on communications. * **VOICE (Radiotelephony):** 4125 kHz, 8291 kHz, and 16420 kHz are established international maritime radiotelephony working frequencies. They are used for subsequent communications after initial contact, often initiated via DSC or distress frequencies. * **SITOR (NBDP - Narrow-Band Direct Printing):** 2174.5 kHz, 6268 kHz, and 12520 kHz are recognized international maritime SITOR (NBDP) working frequencies. These are used for automated text-based communication. The other options are incorrect because they frequently confuse distress *calling* frequencies (like 2182 kHz for voice distress, or 6215 kHz, 8414.5 kHz, 12290 kHz for DSC distress) with follow-on working frequencies, or they misassign modes to frequencies (e.g., listing a voice frequency as a SITOR frequency). Follow-on communications occur on designated working channels *after* an initial alert or call on a specific calling/distress frequency.