The correct option is D Charcoal was too delicate and any form of impurities affected the purity of iron.
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Charcoal was produced by burning trees in the forests. With extensive deforestation, the forest area got reduced. Charcoal was fragile, and transporting it to long distances was a difficult process. It sometimes had impurities, due to which it could not generate high temperatures, resulting in the production of low-quality iron.