GRE Reading Comprehension: OG/PP2-GRE阅读OG/PP2 - 82QG1O5P1AQ654TOL

Centuries ago, the Maya of Central America produced elaborate, deeply cut carvings in stone. The carvings would have required a cutting tool of hard stone or metal. Iron-ore deposits exist throughout Central America, but apparently the Maya never developed the technology to use them and the metals the Maya are known to have used, copper and gold, would not have been hard enough. Therefore, the Maya must have used stone tools to make these carvings.