20 points for your time!which relation is a function? a. {(1, −7), (2, −8), (−2,  7), (1, 8)} b. {(−2, 2), (−7, 7), (−1,  1), (−8, 8)} c. {(−2, 1), (−7, −1), (2,  8), (−7, −8)} d. {(−2, 1), (−2, 2), (−2,  7), (−2, 8)} provide evidence/proof on how you got the answer! !

For a relation to be function, every x value should have its unique image in    co-domain. If x is related to more than one y value, then that relation is not a function 
In 1, as you can see, 1 related to -7 as well as 8. Which means 1 has two images viz. -7 and 8. But for a relation to be function, x should have only one image. Thus, it is not a function.
The worst is the 4th one in which -2 has 4 images. 
Therefore, only relation B is a function.