Does this set of ordered pairs represent a function? why or why not?

{(-1,5), (0, -3), (2,,0), (7,5)}

a. no, because one x-value corresponds to two different y-values.

b. yes, because there are two x-values that are the same.

c. no, because two of the y-values are the same.

d. yes, because every x-value corresponds to exactly one y-value.