The equation of motion of a system subjected to base excitation, \(y(t)\), is given by

a. \(m \ddot{x}+c \dot{x}+k x=-m \ddot{y}\)

b. \(m \ddot{z}+c \dot{z}+k z=-m \ddot{y} ; z=x-y\)

c. \(m \ddot{x}+c \dot{x}+k x=-m \ddot{z} ; z=x-y\)