Answer:
16. a, research
Explanation:
you should form your hypothesis on research because based on what you researched is what will help you try predict the outcome of the experiment
D.theory.
Hypothesis is an idea or explanation of something that is based on a few know facts but that has not yet been proved to be true or correct.
While a theory is a formal set of ideas that is intended to explain why something happens or exists.
Try, Dinosaurs, birds. fish, reptiles. amphibians.
Your answer would be valence electrons, i believe.