(A) Plasmodium → Unicellular parasitic protozoan that causes malaria.
(B) Protozoa → Single-celled eukaryotic organisms by definition.
(C) Spirogyra → Multicellular filamentous green algae forming chains of cells.
(D) Leishmania → Unicellular parasitic protozoan that causes leishmaniasis.
Hence, Option 2: (A), (B) and (D) only → Spirogyra is the only multicellular organism among the given options as it exists as filamentous colonies, while Plasmodium, Protozoa, and Leishmania are all unicellular protozoans → correct