1. **Stating the problem:** We need to determine which of the given graphs represent a function. 2. **Recall the definition of a function:** A relation is a function if every input $x$ has exactly one output $y$. 3. **Use the vertical line test:** If a vertical line intersects the graph more than once at any point, the graph is not a function. 4. **Analyze each graph:** - Graph 1 (circle): A vertical line through the circle intersects it twice at many points, so it is **not a function**. - Graph 2 (piecewise linear): Each vertical line intersects the graph at most once, so it **is a function**. - Graph 3 (parametric with two branches): Vertical lines intersect the graph twice in some places, so it is **not a function**. - Graph 4 (curve with jump/removable discontinuity): Despite the discontinuity, each vertical line intersects the graph at most once, so it **is a function**. 5. **Final answer:** Graphs 2 and 4 represent functions.