When should a lifeguard use a rescue boat?

Using a rescue boat is appropriate when the victim is too far from the pool's edge to reach safely, as stated in the correct answer. This situation arises in circumstances where a lifeguard may be unable to swim directly to the victim due to distance, water conditions, or safety concerns. The rescue boat allows the lifeguard to reach the victim more effectively and safely, minimizing the risk to themselves and ensuring a better outcome for the person in distress.

The other choices may not reflect the best practices for lifeguarding. For example, using a rescue boat during any rescue regardless of conditions could pose additional risks, especially in calm water with easily reachable victims. Similarly, only using a boat under the instruction of a supervisor may not capitalize on immediate opportunities for rescue when needed. It's important for lifeguards to make real-time decisions based on the situation they are facing, prioritizing the safety of all individuals involved.