Consider the feedback system shown in the figure. The Nyquist plot of $G(s)$ is also shown. Which one of the following conclusions is correct?
- $G(s)$ is an all-pass filter
- $G(s)$ is a strictly proper transfer function
- $G(s)$ is a stable and minimum-phase transfer function
- The closed-loop system is unstable for sufficiently large and positive $k$