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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 _____________.

1. $– 4 \leq K \leq \frac{9}{4}$
2. $– 3 \leq K \leq \frac{9}{2}$
3. $– 6 \leq K \leq \frac{5}{4}$
4. $– 5 \leq K \leq 0$