Which of the following is a function? a. {(1,1), (2,5), (-2,5), (1,-1)} b. {(-1,1), (-2,2), (-3,3), (-4,4)} c. {(-1,1), (-1,2), (-1,3), (-1,4)} d. {(-1,1), (-2,1), (-1,3), (-4,1)}

Hey! 
So a function can not have the domain(the x coordinate) repeated in the whole function.
So that eliminates A because 1 is repeated
It eliminates C because -1 is repeated
It also eliminates D because -1 is repeated
So the answer is B!
Hope this helps!

Cbecause they are equal so that means it is the same on both sides? ! hope this