The correct option is C Ernst Haeckel
The three kingdom classification was proposed by Ernst Haeckel. He classified organisms into the following three groups:
i) Protista- It contained unicellular organisms like protozoans, fungi, lichens, bacteria, diatoms.
ii) Plantae- It contained plants.
iii) Animalia- It contained animals.
But this system of classification also had limitations and is not widely accepted.