9. Which of the following relations are functions? Choose all that apply. Assume that each different variable has a different value.
{(a, b),(ba),(C, C),(e, d)}
{(1,4),(c, d).(0,6)
{(6.b).(c, d).(2.c).(4.a)
{(a, b).(5.c).(c, d).(d.)