Concept:An organ is a structure made up of different tissues that work together to perform a specific function.Explanation:The kidney is an organ because it consists of several tissues, such as epithelial tissue and muscle tissue, working as one unit.A waterleaf plant is a whole organism, not just an organ.A virus particle is not cellular and does not have tissues.A spermatozoon is a single cell, not an organ.Answer:C. kidney