Annelids, like the earthworm, and arthropods, like insects or spiders, have three main structures in their nervous systems:
a. a brain, a dorsal nerve cord, and a ventral nerve cord.
b. a brain, segmented ganglia, and a ventral nerve cord.
c. segmented ganglia, a dorsal nerve cord, and a ventral nerve cord.

This is the diveristy of ecosystems natural communites and habits it is the variety of ways that species interact with each other and their environment

How is ribosomal rna useful as a molecular clock? a. a large portion of the dna ring is not vital to structure or function, allowing it to accumulate neutral mutations. b. its rate of mutation increases over time as organisms continue to evolve and differentiate from each other. c. a slow mutation rate makes it useful for determining evolutionary relationships between ancient species. d. it is only found in select organisms, making it easier to compare relationships between species that have it.

The diagram shows the layers of earth. convection currents in which region influence the movement of tectonic plates