The correct option is D Protista
Slime molds are saprophytic protists belonging to the class of myxomycetes. They are neither a plant nor an animal. Though it resembles a fungus, it is not one.
In Whittaker’s Five Kingdom Classification slime molds were placed under the Kingdom Protista because they share some common characteristics with the other organisms which belong to this kingdom. Slime molds are eukaryotic organisms with the presence of cell wall and nuclear membrane. Their body organization is cellular and they exhibit heterotrophic mode of nutrition.