The correct option is A Monera
Spirulina belongs to kingdom monera. It is a spirally coiled free floating filamentous blue green alga or cyanobacterium of upto 0.5 mm length. It can grow both autotrophically and heterotrophically. This cyanobacterium is rich in protein. It also contains minerals, vitamins and essential fatty acids. Because of its beneficial nature, Spirulina is used as food additive in the form of powder, pill or tablet. It is also used as manure. It is helpful in reclamation of usar soils.