Question

Which expressions are polynomials? Select each correct answer.

Answer 1

Only 20x^2+y and 20x^2 are polynomials.

Answer 2

Each of these is a polynomial.

A polynomial is the sum or difference of one or more monomials.  A monomial is a variable, a constant, or the product of variables and constants.  Each of these is a monomial, so it is a polynomial as well.