An electromechanical closed –loop control system has the transfer function C(s)/R(s) = k/s (s2 + s +1) (s+ 4) +k. Which one of the following is correct?

(A) The system is stable for all positive values of k (B) The system is unstable for all values of k (C) The system is stable for values of k between zero and 3.36 (D) The system is stable for values of k between 1.6 and 2.45