Medieval China Practice Test

Blowing air into molten iron is a way to reduce its carbon content and impurities, turning brittle cast iron into steel. The oxygen from the air reacts with carbon and other impurities, forming gases that escape and leaving behind an iron–carbon alloy with just the right amount of carbon. That alloy is steel, which is stronger and more malleable than cast iron. The other options describe crafts or inventions (papermaking, the compass, woodblock printing) and aren’t about producing a metal alloy, so they don’t fit the process described.