Consider the liquid-level control system depicted in Figure 4(a) with the associated block diagram given in Figure 4(b). The objective of this control system is to follow a zero set point, i.e., X(s) 0. The system experiences a step disturbance D(s) of magnitude Do. Which of the following con trollers Ge(s) (if any) would meet the control system objective with zero steady-state error: (a) proportional controller or (b) integral controller? Controllen D(s) RCs+ Distrubance D E(s) G.(s) + R RCs+ .) ) C (a) (b)