Which of the following is a one-to-one function? a. y=[x] b. f(x)={5x-1: x< -2 x-9: x> (or equal to) -2 c. y= ixi d. f(x)={4: x< 0 5: 0< (or equal to)x< (or equal to)2 6: x> 2 i think it's a but i'm really not positive