This answer is correct because throughout the story, the lifeguard explains various rules that swimmers should follow in order to stay safe. The lifeguard emphasizes the importance of following these rules and warns of the dangers that can arise from reckless behavior. This lesson is reinforced by the examples provided in the story, such as the lifeguard rescuing a swimmer who ignored the rules and got into trouble. Therefore, the lesson that the reader can learn from "Lifeguard Rules" is that although pools are fun, reckless behavior can be dangerous.
