Can you help me choose the correct one? Thank you in advance

Find the x-values of all points where the function has any relative extrema. Find the value(s) of any relative extrema. f(x) =x4 - 18x2+81 Select the correct choice below and, if necessary, fill in any answer boxes within your choice. K O A. There are no relative minima. The function has a relative maximum of at x = (Use a comma to separate answers as needed.) O B. There are no relative maxima. The function has a relative minimum of at x = (Use a comma to separate answers as needed.) O C. The function has a relative maximum of at x = and a relative minimum of at x = (Use a comma to separate answers as needed.) O D. There are no relative extrema