Explanation: VHF Channel 16 is the international distress, urgency, safety, and calling frequency. Maritime regulations, particularly under the Global Maritime Distress and Safety System (GMDSS), generally mandate a continuous watch on Ch-16 for all vessels at sea (A). However, specific exemptions exist for vessels in certain scenarios. A vessel operating in an A1 sea area, subject to the Bridge-to-Bridge Radiotelephone Act, and within a Vessel Traffic Service (VTS) system, may be exempt from the Ch-16 watch. This applies provided the vessel actively monitors both VHF Ch-13 (for navigational safety and bridge-to-bridge communications) and the designated VTS working channel (B). This exception prioritizes immediate navigational communication in busy port approaches. Outside these specific A1/VTS exemptions, particularly in sea areas A2, A3, and A4, where vessels are further offshore and potentially rely on MF, HF, or satellite systems for long-range distress, the Ch-16 watch remains compulsory at all times (C). Since all three statements accurately describe true aspects of Ch-16 watch requirements and their specific exceptions, "All of the above" is the correct answer.