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A certain system has transfer function $G(s)=\frac{s+8}{s^{2}+\alpha s-4}$, where $\alpha$ is a parameter. Consider the standard negative unity feedback configuration as shown below.

Which of the following statements is true?

- The closed loop system is never stable for any value of $\alpha$.
- For some positive values of $\alpha$, the closed loop system is stable, but not for all positive values.
- For all positive values of $\alpha$, the closed loop system is stable.
- The closed loop system is stable for all values of $\alpha$, both positive and negative.