The loop-gain function L(s) of a control system with unity feedback is given to be L(s) = $\frac{k}{(s + 1)(s + 2)(s + 3)}$, where k >0. If the gain cross-over frequency of the loop-gain function is less than its phase cross-over frequency, the closed-loop system is
- unstable
- marginally stable
- conditionally stable
- stable
