The symbol D represents the differentiation operator d/dt. Which two operators are NOT the same? a. D + 3 and 3+ D b. D3 - 3D2 + 3D - 1 and (D - 1) c. (D-5)(D+2) and (D+2)(D-5) d. (D+t) D and D(D+1) e. none of the above.