When is a sound signal required according to navigational rules?

Answer: B — When meeting or crossing inland waters

A sound signal is required when two vessels are meeting or crossing, particularly in narrow channels and when navigating inland waters, as it helps to avoid collisions and facilitates safe navigation. The COLREGs specify that sound signals are a crucial form of communication between vessels, particularly in situations of potential risk. When vessels are approaching each other or are about to cross paths, sound signals help indicate intentions, such as passing on the port or starboard side, which is essential for maintaining safety and situational awareness. This requirement is primarily to enhance safety among vessels that may not have a clear line of sight, thereby minimizing the chances of accidents. In contrast, the other scenarios listed do not universally demand sound signals. For example, sound signals are not exclusively required for international waters, overtaking, or when anchored. Each of these situations has its specifics concerning sound signaling, but they do not necessitate a sound signal as a rule across all circumstances as is the case in meeting or crossing situations.