Evolution has been tested in various ways. genetic, fossil, anatomical, physiological and behavioral studies all confirm that evolution is the mechanism of the origin of species. thus, in science evolution is considered a scientific

Theory.

Explanation:

Evolution may be defined as the changes in  the species characteristics with respect to time. Different evidences like fossil evidence, genetic evidence and the behavioral study is used for the evolutionary study.

Scientific theory may be defined as the explanationary aspect of the world's phenomena. The scientific evidence, experiment and results are important to make a scientific theory. The phenomena of the evolution can be explained by the scientific theory.

Thus, the answer is theory.  

well, that's easy; the answer's c, "it reduces contamination of the water and substrate of the estuary."