1. **State the problem:** We are given three tables of $x$ and $y$ values and asked which tables represent functions and how to tell. 2. **Recall the definition of a function:** A function assigns exactly one output $y$ for each input $x$. This means no $x$ value can be paired with more than one $y$ value. 3. **Analyze Table A:** The pairs are $(1,7), (2,7), (3,12), (4,5)$. Each $x$ value is unique and appears only once, so each input has exactly one output. 4. **Analyze Table B:** The pairs are $(-1,5), (3,8), (7,2), (3,5)$. The input $x=3$ appears twice with different outputs $8$ and $5$. This violates the function rule. 5. **Analyze Table C:** The pairs are $(0,1), (1,2), (1,3), (3,4)$. The input $x=1$ appears twice with different outputs $2$ and $3$. This also violates the function rule. 6. **Conclusion:** Only Table A represents a function because each input $x$ has exactly one output $y$. Tables B and C do not represent functions because some inputs have multiple outputs. **Final answer:** Table A represents a function; Tables B and C do not.