If the function $f : \mathbb { R } \rightarrow \mathbb { R }$ is defined by $f ( x ) = | x | ( x - \sin x )$, then which of the following statements is TRUE?\\
(A) $f$ is one-one, but NOT onto\\
(B) $f$ is onto, but NOT one-one\\
(C) $f$ is BOTH one-one and onto\\
(D) $f$ is NEITHER one-one NOR onto