Concept:Chikungunya is an infectious disease transmitted by mosquitoes, and its causal agent is a virus.Explanation:Viruses are tiny intracellular parasites that contain either RNA or DNA, covered by a protein coat. They are inactive outside a host cell and require a living cell to multiply. The chikungunya virus belongs to this category. Non-chlorophyllous bacteria are single-celled organisms, but they do not cause chikungunya. Nematodes are parasitic roundworms, and fungi are eukaryotic organisms; both are incorrect for this disease.Answer:C. Virus