What is a scientific theory?

• A. A guess not supported by evidence.
• B. A simple description of a phenomenon.
• C. A collection of facts.
• D. A well-substantiated explanation of an aspect of the natural world based on a body of evidence.

Answer: (D)

A scientific theory is a well-substantiated account of a natural phenomenon that brings together a wide range of observations and experimental results into a coherent framework. It's not a guess, and it's not just a single observation or a simple description of what happens. It rests on evidence collected and tested over time, and it makes testable predictions that can be evaluated with further experimentation. The best choice captures that combination: a theory is an account supported by evidence about how and why something works in the natural world. For example, the theory of evolution explains the diversity of life by proposing mechanisms supported by data from genetics, fossils, and direct observation. It isn’t simply a pile of facts, nor is it merely a description of what you see; it ties the facts together to show how they fit and why they occur. The other ideas fall short because a guess without evidence lacks a solid basis; a simple description doesn’t explain why things happen; a collection of facts doesn’t organize them into a framework that shows how they relate.