{(3, 9), (4, 8), (–7, 4), (0, 4), (2, 4), (3, 5), (–3, 8)}
a. Yes, each x-value is paired with exactly one y-value.
b. No, there is a y-value paired with more than one x-value.
c. No, there are no negative y-values.
d. No, there is an x-value paired with more than one y-value.