Which would best be used as an index fossil? O A. alligator bones, because they have lived a long time with relatively few changes in body structure
O B. petrified wood, because it clearly shows the parts of the wood replaced by minerals
O C. sedimentary rock, because it is found in horizontal layers created in succession
O D. trilobites, because they lived for a short period of time and then became extinct

The image shows the evolution of a species of fish. a few fish from a population developed different social behaviors and evolved into different species. two fish according to the image, the fish underwent . the new species of fish had mating seasons that were different from that of the original fish. because of the differences in mating seasons, the fish underwent reproductive isolation. this mode of isolation would be .