The correct answer is A. How gravity works
Explanation:
The word "theory" is a term that emerged in Ancient Greece where it was used to refer to the action of observing, contemplating or studying. However, nowadays, theory refers to a set of statements that explain a phenomenon. Indeed, a scientific theory is a proved explanation that describes how and why a phenomenon occurs that emerges from multiple and consistent experiments and observations. According to this, "How gravity works" is the option that describes a scientific theory because this focuses on explaining the way and reasons a phenomenon occurs which is the purpose of scientific theories.