Answer:
The "Cambrian Explosion" refers to the sudden appearance in the fossil record of complex animals with mineralized skeletal remains. It may represent the most important evolutionary event in the history of life on Earth.
Explanation:
It is based on shared characteristics
I would go with B & D because they change over time and they can go extinct like those big octopus in the oceans, they are rare to see in my opinion because they can blend in with other things that keeps them away from danger.
Alleles. Alleles are the "same" genes, but provide a variation of the intended function.
