Step-by-step explanation:
Polynomials are closed under an operation if it produces a polynomial.
5x⁴, x² + 2x + 1 and x³ - 10x³ + 28x - 15
are all polynomials of x.
x - 3 + (-3)/(x - 2) is not a polynomial because x can be found in the denominator of a fractional term.
The answer is Option A.
