Let $f(x)$ be the function defined by $f(x)=x^3-147x+135.$ On which

of the following intervals is $f(x)$ decreasing?

$(-,-7)$ and $(7,)$

$(-7,7)$

$(-\sqrt[\phantom{2}]{\frac{147}{2}},\sqrt[\phantom{2}]{\frac{147}{2}})$

$(-,-\sqrt[\phantom{2}]{\frac{147}{2}})$ and $(\sqrt[\phantom{2}]{\frac{147}{2}},)$

$(-,-7)$