The graph below does not represent a function because it fails the vertical-line test.

which is the best explanation of why a graph that fails the vertical line test does not represent a function?
a. if a vertical line intersects a graph more than once, this indicates that there are multiple points with the same y-value. a function cannot have repeated y-values.
b. on a vertical line, one x-value is paired with many y-values. a function cannot have one x-value paired with different y-values, so a vertical line is not a function.
c. the points where a vertical line intersects a graph have the same x-value but different y-values. the graph of a function cannot have points with the same x-value but different y-values.
d. the relation represented by a vertical line maps many x-values to the same y-value. this kind of mapping is not a function. so if a graph intersects a vertical line more than once, that graph is not a function either.