Which group of organisms is believed to be among the earliest to evolve on Earth?
A. Reptiles.
B. Protozoans.
C. Arthropods.
D. Coelenterates.
Protozoans are a group of animal-like unicellular Protists. From unicellular organisms, multicellular organisms theoretically arose. Coelenterates, of which the Hydra and jellyfish belong, would be more advanced than protozoans but more primitive than arthropods, of which the grasshoppers belong. The reptiles are more advanced than the arthropods.