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.  

before, trains worked using the steam engine. thus, it uses heat so it is crucial to apply heat balance. the steam engine absorbs energy during the stage of boiling water. so, this is the endothermic reaction. when the steam is used to work the piston, it has to release this energy through running the train. the excess energy is released as an exhaust to the chimney. this is the exothermic process because it releases energy to the surroundings.