The open-loop transfer functions with unity feedback are given below for different systems. 1. (mathrm{G}(s)=frac{2}{s+2}) 2. (G(s)=frac{2}{s(s+2)})

Question:

The open-loop transfer functions with unity feedback are given below for different systems.
1. $\mathrm{G}(s)=\frac{2}{s+2}$
2. $G(s)=\frac{2}{s(s+2)}$
3. $G(s)=\frac{2}{s^{2}(s+2)}$
4. $\mathrm{G}(s)=\frac{2(s+1)}{s(s+2)}$

Among these systems, the unstable system is
(a) 1
(b) 2
(c) 3
(d) 4