Which of the following is not a quadratic equation?

A quadratic equation must be expandable into the standard form $a{x}^2+bx+c=0$, where $a\ne 0$ (the degree of the polynomial must be 2).Let's test the options:Option A:
$$3x^2+15x-11=2x^2-4x+6$$
$$x^2+19x-17=0(\text{This is a quadratic equation})$$
Option B:
$$4x^2+12x+7=4x^2-44x+9$$
Cancel $4x^2$ from both sides:
$$12x+7=-44x+9$$
$$56x-2=0(\text{This is a linear equation, NOT quadratic})$$
Option C:
$$x^2+2x-15=2x^2-5x+11$$
$$x^2-7x+26=0(\text{This is a quadratic equation})$$
Option D:
$$4x^2-6x-9=0(\text{This is already in standard quadratic form})$$