221. Which is one of the signals, other than a distress signal, that can be used by a rescue boat to attract attention?

A searchlight is the correct answer because it is standard rescue boat equipment used for visibility and locating survivors, and is not a recognized distress signal. Internationally recognized distress signals, such as orange smoke, burning barrels, and red star shells, are reserved for emergencies to avoid diverting rescue resources and causing confusion. Rescue boats should use non-distress signals like searchlights for routine attention-getting and reserve distress signals for situations where the boat itself is in danger.