1. **State the problem:** Determine which of the given graphs represents a function and justify the answer. 2. **Recall the definition of a function:** A function assigns exactly one output $y$ for each input $x$. Graphically, this means that for every vertical line drawn on the graph, it should intersect the graph at most once (Vertical Line Test). 3. **Analyze graph (a):** The graph is a horizontal line $y=1$. For every $x$ value, there is exactly one $y$ value, which is 1. 4. **Apply the Vertical Line Test to graph (a):** Any vertical line will intersect the horizontal line $y=1$ exactly once. 5. **Analyze graph (b):** The graph is a vertical line $x=1$. For the input $x=1$, there are multiple $y$ values (2, 0, -2, etc.). 6. **Apply the Vertical Line Test to graph (b):** A vertical line at $x=1$ intersects the graph infinitely many times, failing the test. 7. **Conclusion:** Graph (a) represents a function because it passes the Vertical Line Test. Graph (b) does not represent a function because it fails the test. **Final answer:** Only graph (a) represents a function.