Which of the following shows that polynomials are closed under subtraction when two polynomials, (5x2 + 2x − 6) − (3x2 − 6x + 2), are subtracted? 2x2 − 4x − 4; will be a polynomial 2x2 − 4x − 4; may or may not be a polynomial 2x2 + 8x − 8; will be a polynomial 2x2 + 8x − 8; may or may not be a polynomial