8. Let $x$ be a variable that takes real values, and let $f ( x ) = x ^ { 3 } - 3 x$. Which of the following statements is/are true?\\
(a) $f ( x )$ has a local maximum at $x = - \sqrt { 3 }$\\
(b) $f ( x )$ has a local maximum at $x = - 1$\\
(c) $f ( x )$ has a local minimum at $x = \sqrt { 3 }$\\
(d) $f ( x )$ has a global minimum at $x = 1$\\