Answer:
B protista
Step-by-step explanation:
The cell is unicellular, so it can not be an animal, which are all multicellular.
It contains a nucleus, which means it cannot be prokaryotic (it cannot be bacteria)
The cell is autotrophic, which means it cannot be a fungus, which are heterotrophs
Therefore, the organism must be a protist, so the answer is B, protista.