While underway, if you are required to have a radiotelephone, you must maintain a continuous listening watch on which of the following channels?

Correct Answer: Option D — 16 (156.8 MHz)

33 CFR 26.04 requires vessels to maintain a continuous listening watch on Channel 16 (156.8 MHz) while underway. This frequency is the international distress, safety, and calling channel, ensuring that vessels can receive urgent alerts, distress signals, and safety information from other ships or shore stations.