means, for every 1 input, there is 1 coresponding output
normally x is input and y is output in form (x,y)
so just look for the option(s) that has/have every first number repeat with only 1 2nd number
A. -7 repeats with 5 and -3, not a function
B. no repeats of first number (6,-8) and (-5,-8) are fine because first numbers don't repeat, das is funciton
C. no repeats, function
D. no repeats, function
answer is B,C,D