Which of the following equations demonstrate that the set of polynomials is
not closed under the certain operations?
A. Subtraction: (3x^4+x^3)-(-2x^4+x^3)=5x^4
B. Addition: (x^2+x)+(x+1)=x^2+2x+1
C. Division: (x^2-5x+3)÷(x-2)=x-3+-3/x-2
D. Multiplication: (x^2-5x+3)(x-5)=x^3-10x^2+28x-15