To which group do the following organisms belong and give one reason for each:
$(a)$ Cyanobacteria
$(b)$ Euglena
$(c)$ Ulothrix

(N/A) Cyanobacteria belongs to the kingdom $Monera$. The reason is that they are prokaryotic organisms and do not have a well-defined nucleus or membrane-bound cell organelles.
$(b)$ Euglena belongs to the kingdom $Protista$. The reason is that they are unicellular,eukaryotic organisms that possess chloroplasts for photosynthesis.
$(c)$ Ulothrix belongs to the kingdom $Plantae$ (specifically the division $Thallophyta$). The reason is that their body is not well-differentiated into roots,stems,and leaves; they are multicellular,eukaryotic,filamentous,and photosynthetic.