Right choice is (a) \(\frac{sinhθ}{z^2-2z coshθ+1} \)
For explanation: The first step to solve this is to expand the function sinhnθ. The expansion of this function is of the form a^n. First we have to find the Z-Transform of 1 and then we have to use damping rule. To, get the answer, we take L.C.M.