Concept:A natural magnet is a naturally occurring substance that already has magnetic properties.Explanation:Lodestone is a naturally magnetized mineral called magnetite, with the formula Fe3​O4​.It attracts iron and can align itself with Earth’s magnetic field.Copper, silicon, and zinc are not natural magnets.Therefore, among the given options, lodestone is the natural magnet.Answer:D. Lodestone (Fe3​O4​)