1. **State the problem:** We are given three curves A, B, and C and need to identify which curve is not a function of $x$. 2. **Recall the definition of a function of $x$:** A curve represents a function of $x$ if for every value of $x$, there is exactly one corresponding value of $y$. 3. **Analyze each curve:** - Curve A: It increases smoothly and crosses the $x$-axis once, showing one $y$ for each $x$. This matches the definition of a function. - Curve B: It decreases then increases, but for each $x$ there is only one $y$ value, so it is also a function. - Curve C: It loops or crosses the same vertical line multiple times, meaning for some $x$ values there are multiple $y$ values. 4. **Conclusion:** Curve C is not a function of $x$ because it fails the vertical line test (a vertical line intersects the curve more than once). **Final answer:** Curve which is not a function of $x$: C ✔ Reason: Curve C has multiple $y$ values for some $x$ values, so it is not a function of $x$.