During science class, students were instructed to develop a dichotomous key (a tool that allows the user to determine the identity of items in the natural world) in order to classify organisms into one of the six kingdoms of life. Ms. King, their teacher, provided them with this diagram. According to the diagram, the BEST way to separate all living things into two main groups would be to consider A) method of reproduction. B) consumer versus producer. C) cell type, prokaryotic versus eukaryotic. D) organization, unicellular versus multicellular.