Yeast cells, plant cells, and mammal cells all share many similarities in cell signaling. This provides evidence that: a. cell-signaling mechanisms are only found in organisms that use methods of sexual reproduction
b. intercellular communication evolved as a way for multicellular organisms to coordinate cell functions
c. eukaryotic cells use signal transduction pathways while prokaryotic cells use a more primitive form of signaling
d. signal transduction pathways appeared in cells before the evolution of multicellular organisms