The correct option is C Amoeba proteus
A parasite is an organism that has adapted to invade and live in cells and tissues of other organisms. Amoeba proteus is a free living organism and capable of independent existence. While Plasmodium vivax, Trypanosoma gambiense and Entamoeba histolytica are parasitic protozoans.
Plasmodium vivax causes malaria.
Trypanosoma gambiense causes sleeping sickness.
Entamoeba histolytica causes dysentery.