Chọn phương án C.

\(\begin{aligned}
\lim\left(9-5n-2n^3\right)&=\lim n^3\left(\dfrac{9}{n^3}-\dfrac{5}{n^2}-2\right)\\
&=-\infty.
\end{aligned}\)

Vì \(\begin{cases}
\lim n^3&=+\infty\\
\lim\left(\dfrac{9}{n^3}-\dfrac{5}{n^2}-2\right)&=-2<0.
\end{cases}\)