図のシステム伝達関数はどれか。
1: $\frac {1}{G\left( s\right) H\left( s\right) }$
2: $\frac {G\left( s\right) }{1-G\left( s\right) H\left( s\right) }$
3: $\frac {G\left( s\right) }{1+G\left( s\right) H\left( s\right) }$
4: $\frac {G\left( s\right) H\left( s\right) }{1-G\left( s\right) H\left( s\right) }$
5: $\frac {G\left( s\right) H\left( s\right) }{1+G\left( s\right) H\left( s\right) }$