The correct answer is: D. a validated hypothesis.
A theory is a well-substantiated explanation of some aspect of the natural world, based on a body of facts that have been repeatedly confirmed through observation and experiment. Such fact-supported theories are not “guesses” but reliable accounts of the real world. The theory of biological evolution is more than “just a theory.” It is as factual an explanation of the universe as the atomic theory of matter or the germ theory of disease. Our understanding of gravity is still a work in progress. But the phenomenon of gravity, like evolution, is an accepted fact.
An assumption is a statement that is taken for granted or accepted as true without proof. An “if-then” proposition is a statement that describes the relationship between two events. A hypothesis is a tentative statement about the natural world leading to deductions that can be tested. A validated hypothesis is a hypothesis that has been tested and found to be true.
In conclusion, a theory is a validated hypothesis. It is a well-substantiated explanation of some aspect of the natural world, based on a body of facts that have been repeatedly confirmed through observation and experiment.