Consider an even polynomial $p(s)$ given by
$$p(s) = s^{4} + 5s^{2} + 4 + K,$$
where $K$ is an unknown real parameter. The complete range of $K$ for which $p(s)$ has all its roots on the imaginary axis is _____________.
- $ – 4 \leq K \leq \frac{9}{4}$
- $ – 3 \leq K \leq \frac{9}{2}$
- $ – 6 \leq K \leq \frac{5}{4}$
- $ – 5 \leq K \leq 0$