The correct option is C Robert Hooke
Robert Hooke observed a thin slice of cork under the compound microscope he had developed. He noticed small box-like structures and called them “cells”, a term which is derived from the Latin word “cellula” meaning “small compartment”. Leeuwenhoek observed blood cells as well as single-celled organisms with the help of a simple microscope he had developed and recognised them as living units. However, he did not call them cells. Matthias Jakob Schleiden, Theodor Schwann and Rudolf Virchow postulated the Cell theory.