They used marble, bronze, and clay
The Mound Builders used metal tools, and were probably metal builders. Based on that information I would say the answer is B.Copper, because copper is a metal.
I personally think pop music appeals to younger individuals because well pop bands are usually trying to appeal to kids and pop bands have clean, appropriate, language used in their songs so its all ages. I think the industry promoted this idea by thinking of kids because today in the music industry, its all about trap, hip hop, and R&B and those genres are not kid friendly so maybe the industry thought of kids for a change or maybe did service by making music for kids or maybe are doing it for the glory and fame.
Face and body....................................
