等差数列 $\left\{a_{n}\right\}$ 的前 $n$ 项和为 $S_{n}$, 若公差 $d>0,\left(S_{8}-S_{5}\right)\left(S_{9}-S_{5}\right)<0$, 则 ( )
解析: $\because$ 公差 $d>0,\left(S_{8}-S_{5}\right)\left(S_{9}-S_{5}\right)<0$,

$\therefore S_{9}>S_{8}$,
$\therefore S_{8}<S_{5}<S_{9}$,

$\therefore a_{6}+a_{7}+a_{8}<0, \therefore a_{6}+a_{7}+a_{8}+a_{9}>0$,

$\therefore a_{7}<0, a_{7}+a_{8}>0$,

$\therefore\left|a_{7}\right|<\left|a_{8}\right|$,

故选: D.