So abiotic means nonliving, so the only abiotic option is B. the gravel on the bottom of the aquarium.
Answer:
Charles Darwin's theory of evolution states that evolution happens by natural selection. Individuals in a species show variation in physical characteristics. As a consequence those individuals most suited to their environment survive and, given enough time, the species will gradually evolve
hope this helps!
<span>The male's feathers do not get longer and longer each generation because they would reach a point in which the feathers would hinder their survival. If the females preferred feather trains that would help males fly, then males would likely have much shorter feather trains.</span>
