2. Which one of the following functions is not one to one? A)f:Z → Z, f(x) = X-1 B)f:N → N, f(x) = 3x + 4 C)f: R → R, f(x) = 2x - 3 D)f: RR, (x) = x2 E)f: R → R, f(x) = 3x2 -​