A.

This is a quadratic equation of the form hence i.e. of degree 2 (a ≠ 0, a, b, c are real numbers).

B.

using

This is a quadratic equation of the form i.e. of degree 2 (a ≠ 0, a, b, c are real numbers).

C. using

This is not quadratic since it is not of the form i.e. of degree 2 (a ≠ 0, a, b, c are real numbers).

D.

using

This is a quadratic equation of the form i.e. of degree 2 (a ≠ 0, a, b, c are real numbers).