Answer:
The correct answer is D {(-9, 8), (-5, -8), (-7, 8), (-6, -8)}
Explanation:
Set A is not a function because there are 2 ordered pairs in which x = -12. 
Set B is also not a function because there are 2 ordered pairs in which x = 8, and x = -8. 
Set C is also not a function because all of the ordered pairs have the same x value of 13. 
That is why Set D is the correct answer. 
In the attached images, I graphed the Vertical Line Test I did on all sets to show why Set D is the only function.