Consider a unity negative feedback system with a loop transfer function (with nominal values)

L(s) = Ge(s)G(s) K s(sa)(s+b) 4.5 s(s + 1)(s + 2) Using the Routh-Hurwitz stability analysis, it can be shown that the closed-loop system is nominally stable. However, if the system has uncertain coefficients such that 0.25 a 3, 2 b 4, and 4 K 5, the closed-loop system may exhibit instability. Which of the following situations is true: a. Unstable for a = 1, b = 2, and K = 4. b. Unstable for a 2, b = 4, and K = 4.5. = c. Unstable for a = 0.25, b 3, and K = 5. = d. Stable for all a, b, and K in the given intervals.