Final answer:
A scientific theory is a byproduct of substantial evidence and rigorous testing within the natural world, with 'A. How gravity works' being an example that aligns with the definition of a scientific theory.
Step-by-step explanation:
What is Considered to be a Scientific Theory?
A scientific theory is a well-substantiated explanation of some aspect of the natural world that is acquired through the scientific method and repeatedly tested and confirmed through observation and experimentation. Among the options given, A. How gravity works would be considered a scientific theory. This is because physics explains how gravity works through laws and models encompassing a vast amount of evidence and verification, such as Newton's Law of Universal Gravitation. These laws help us understand the motion of objects and the fundamental aspects of the universe, focusing on how matter interacts with other matter in space and time, making gravity an integral part of physical science. Scientific theories like the theory of gravity have an overwhelming amount of evidence backing their correctness.