Which of the following is NOT a quadratic function?

Select one:
A. (x+5)(2x+5)
B. x^2−2x−19
C. x^3−2x^2−6x/x
D. x(x^2+4x)

The choice that is NOT a quadratic function is choice C. x^3−2x^2−6x/x. I say this because the first variabl, x has a power of 3. That is definetly more than 2. Now, we have to think back to the fact that a quadratic expression is any mathematical expression that the power or degree is just two, not any high, not any lower. Otherwise, any expression that uses a variable in which  the largest exponent or even the expression's power/degree is two is a quadratic expression.

Brainliest please, i need a few more :D