What are the possible numbers of positive, negative, and complex zeros of f(x) = −3x4 − 5x3 − x2 − 8x + 4? a. positive: 2 or 0; negative: 2 or 0; complex: 4 or 2 or 0 b. positive: 1; negative: 3 or 1; complex: 2 or 0 c. positive: 3 or 1; negative: 1; complex: 2 or 0 d. positive: 4 or 2 or 0; negative: 2 or 0; complex: 4 or 2 or 0