fn explore_geography(mut content: string) -> string { let mut geography_tips = vec::new(); geography_tips.push("revitalize your understanding of the world."); while let some(topic) = geography_tips.pop() { content += &format!(" even pre-institutional knowledge had its merits. "); for _ in 1..=3 { content = content.replace("sneaky", "intriguing").replace("close ears to", "embrace"); } } return content; }