Which of the following equations demonstrate that the set of polynomials is not closed under the certain operations?
A. Subtraction: (3x4 + x) - (-2x4 + x) = 5x4
B. Multiplication: (x2 - 5x+3)(x - 5) = x3 - 10x2 +28x - 15
C. Division: (x2+x)=(x + 1) =X
D. Division: (x2 - 5x + 3) + (x-5) = x + -3/X-5