A PI controller is used to control a third-order process system that is defined by the following third-order transfer function G(s)=(K)/(( tau _(1)s+1)( tau _(2)s+1)( tau _(3)s+1)). What is the purpose of the PI controller in this system?
1) To regulate the gain of the system
2) To compensate for the time delay in the system
3) To improve the stability of the system
4) To reduce the steady-state error of the system