* Unicellular: Protists are single-celled organisms.

* Can use photosynthesis: Many protists, like algae, have chloroplasts and can perform photosynthesis.

* Contains DNA in nucleus: Protists are eukaryotes, meaning they have a nucleus that contains their DNA.

While some bacteria can also perform photosynthesis, they are prokaryotes and lack a nucleus. Fungi are multicellular (except for yeasts) and do not perform photosynthesis. Plants are multicellular and also perform photosynthesis.

Therefore, the combination of these traits points to a protist.