Concept:Moulds are microscopic fungi that grow on damp organic matter.Explanation:Stored cereal grains develop mould when moisture is present.Fungi produce spores that germinate quickly in damp, warm conditions.They feed on the nutrients in the grains, causing visible mould growth.Bacteria, viruses, and nematodes are not responsible for mould growth.Thus, the cause of mould on damp cereal grains is a fungus.Answer:B. fungus