I believe that D is the answer to your question, even though this is a complicated one.
I think the answer would be pesticides... i see you selected it though. was that a wring answer?
Answer:
this is a common ... saw incredible similarities between birds and the theropod dinosaurs (especially ... Like all other reptiles, birds have scales (feathers are produced by tissues similar to ... for theropods are often more serious for the "thecodont" pseudo-hypothesis.
Explanation:
Answer - Theory
Reasoning - Your best bet and term to describe the evolution by natural selection is theory as to still scientific theory/research is still ongoing and changes can be made in a different direction.