Cyanobacteria are classified under

1.  Protista

2.  Plantae

3.  Monera

4.  Algae

(C) Monera Kingdom-Monera is one group which exclusively includes all forms of bacteria. All bacteria are prokaryotes and do not have well defined nucleus and other cell organelles.
The other options Protista, Algae and Plantae include eukaryotic and unicellular or multicellular organism.