The correct option is D Fungi
Primary producers are the autotrophs or chemotrophs that can fix the atmospheric carbon dioxide into organic compounds using the energy from Sunlight or oxidation of organic/inorganic compounds respectively. Phytoplankton, algae, mosses and cyanobacteria are producers while fungi are heterotrophs/saprophytes that derive their nutrition from live or dead and decaying organisms. Thus, the correct answer is D.