Find all critical numbers of the function f(x) = x -8x. Then use the second-derivative test on each critical number to determine whether it leads to a local maximum or minimum. Select the correct choice below and, if necessary, fill in the answer box(es) to complete your choice. O A. The critical number(s) is/are at x= There is a local maximum at x = There is no local minimum. (Type an integer or a simplified fraction. Use a comma to separate answers as needed.) There is no local maximum. There is a local minimum at x = O B. The critical number(s) is/are at x = (Type an integer or a simplified fraction. Use a comma to separate answers as needed.) O C. The critical number(s) is/are at x = There is a local maximum at x = There is a local minimum at (Type an integer or a simplified fraction. Use a comma to separate answers as needed.) O D. The critical number(s) is/are at x = There is no local maximum and no local minimum. (Type an integer or a simplified fraction. Use a comma to separate answers as needed.) O E. There are no critical numbers.