The answer is the top-right graph. It represents a function because it passes the vertical line test—every vertical line intersects the graph at most once.

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Related Questions:

1. What is the vertical line test, and how does it determine if a relation is a function?
2. Why does the top-left graph fail to represent a function?
3. How can we represent functions algebraically rather than graphically?
4. What are real-world examples of functions and non-functions?
5. How do domain and range relate to the concept of a function?

Tip: When analyzing graphs, always apply the vertical line test to quickly determine whether the relation is a function.