The set of all values of the parameters $a$ for which the points of minimum of the function $y=1+a^{2} x-$ $x^{3}$ satisfy the inequality $\frac{x^{2}+x+2}{x^{2}+5 x+6} \leq 0$ is
(a) an empty set
(b) $(-3 \sqrt{3},-2 \sqrt{3})$
(c) $(2 \sqrt{3}, 3 \sqrt{3})$
(d) $(-3 \sqrt{3},-2 \sqrt{3}) \cup(2 \sqrt{3}, 3 \sqrt{3})$