答案：C
留意 $\alpha + \beta = k$ 及 $\alpha\beta = 3$。由此，可得
留意 $\alpha + \beta = k$ 及 $\alpha\beta = 3$。由此，可得
$\begin{array}{cl}
& \alpha^3+\beta^3 \\
= & (\alpha+\beta)(\alpha^2-\alpha\beta+\beta^2) \\
= & (\alpha+\beta)[(\alpha+\beta)^2-3\alpha\beta) \\
= & (k)(k^2-3(3)) \\
= & k^3-9k
\end{array}$
