The answer is either B, and you forgot to put in the ^2 in the answer choice, or C, and you forgot to put an x where there is a _ in the question.
Check the actual question (the one you recieved, not the one posted here) and see where the mistakes are. If f(x) = 8x - 4x - x^3, then your answer is C. However, if B is actually -x^3 + x^2 + 3x - 1, then the answer is B.