The answer is the option A: A) 20x^2
The explanation is shown below:
1. The polynomials can't have:
- Fractional exponents.
- Variables in the denominator.
2. As you can see, the option B) 20x^2/y has the variable "y" in the denominator, Therefore, it is not a polynomial.
3. The option C) 20x^2+y^1/2 has a fractional exponent, so it is not a polynomial.