Let f(x)=-x and substitute it to get f (x) = 1/6 x 3.

ABD, OK can be ruled out, leaving only C. If you can't rule out three options, find a simple exception. There is a deep collective thought in this, I hope the landlord will think about it.

Special assignment method is a method that must be mastered deeply, otherwise multiple-choice questions will always be weak points. Mastered the special assignment method, the function multiple-choice question is a pile of slag that can be given points, and it can be done in 2 minutes at most.