Find the intervals on which f is increasing and the intervals on which it is decreasing. f(x) = - x - 4x Select the correct choice below and, if necessary, fill in the answer box(es) to complete your choice. O A. The function is increasing on the open interval(s) and decreasing on the open interval(s) (Simplify your answers. Type your answers in interval notation. Use a comma to separate answers as needed.) O B. The function is decreasing on the open interval(s) The function is never increasing. (Simplify your answer. Type your answer in interval notation. Use a comma to separate answers as needed.) O C. The function is increasing on the open interval(s) The function is never decreasing. (Simplify your answer. Type your answer in interval notation. Use a comma to separate answers as needed.) O D. The function is never increasing nor decreasing