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:$\frac {G\left( s\right) H\left( s\right) }{1+G\left( s\right) H\left( s\right) }$