12. The unit step response of the closed-loop system is:

1.76z + 1.76 a. Y(z) = z + 3.279z+2.76 1.76z + 1.76 b. Y(z) = z3+2.279z20.5194z - 2.76 1.76z+1.76z c. Y(z) = z + 2.279z2-0.5194z - 2.76 1.76z + 1.76z d. Y(z) = 2.279z2-0.5194z-2.76