The correct answer is option 2: Cyanobacteria. Blue-green algae, also known as cyanobacteria, are a group of photosynthetic bacteria that possess chlorophyll-a and phycobiliproteins. They are called blue-green algae because some species can produce blue-green pigments. Cyanobacteria are capable of photosynthesis, similar to plants and algae, but they are prokaryotes and not classified as true algae. Option 1, Eubacteria, is a broader category that includes all bacteria, including cyanobacteria. Option 3, Protozoa, refers to a group of eukaryotic microorganisms, distinct from cyanobacteria. Option 4, Fungi, are a separate kingdom of organisms that are heterotrophic and distinct from cyanobacteria. Thus, the correct option is option 2: Cyanobacteria.