178. Which of the following statements regarding the stability of a feedback control system is correct? (a) Gain margin (GM) gives the complete information about the relative stability of the gain system. (b) Phase margin (PM) gives the complete information about the stability of the system. (c) GM and PM together give information about the relative stability of the system. (d) Gain cross-over and phase cross-over frequencies give the required information about the relative stability of the system.