Note each of them:
Archaea is a single-celled microorganism with no nucleus
Bacteria is a unicellular microorganism with cell walls but lack organelles
Sarcodina is a phylum with temporary extensions of the cell. They can be parasitic.
Protista is an eukaryotic organisms that is not an animal, plant, or fungus.
The organism found is unicellular (rules out Archaea), with cell walls (characteristics of bacteria), and the ability to produce spores.
I believe that Bacteria (B) is your best answer
hope this helps