(don't understand but I think its easy)Which of the following relations is a function? A. {(-3, -1), (-1, -3), (-3, -3), (9, 4), (2, 3)} B. {(1, 7), (2, 8), (4, 5), (0, 0), (3, 5)} C. {(2, 5), (5, 6), (2, 3), (1, 7), (0, 2)} D. {(6, 1), (5, 8), (9, 9), (5, 9), (5, -3)}

Answer:   B. {(1, 7), (2, 8), (4, 5), (0, 0), (3, 5)}Step-by-step explanation:You are right, it is easy. Any relation with a repeated first value is not a function.A has (-3, -1) and (-3, -3), so the value -3 is a repeated first value.C has (2, 5) and (2, 3), so the value 2 is a repeated first value.D has (5, 8), (5, 9), and (5, -3), so the value 5 is a repeated first value.None of A, C, or D is a relation that is a function. The correct choice is B, which has first values 0, 1, 2, 3, 4 -- none of which is repeated._____If you plot points with repeated first values, you find they lie on the same vertical line. If a vertical line passes through 2 or more points in the relation, that relation is not a function. We say, "it doesn't pass the vertical line test." A relation must pass the vertical line test in order to be a function. This is true of graphs of any kind, not just graphs of discrete points.