Match each function with its name.
$$f(x)=x$$
$$\begin{array}{ll}{\text { (a) squaring function }} & {\text { (b) square root function }} & {\text { (c) cubic function }} \\ {\text { (d) linear function }} & {\text { (e) constant function }} & {\text { (f) absolute value function }} \\ {\text { (g) greatest integer function }} & {\text { (h) reciprocal function }} & {\text { (i) identity function }}\end{array}$$