The sequence of transformations that maps triangle ABC to triangle A1 B1 C1 is reflection across the blank

The statement is FALSE.

A constant term is also a polynomial with just one term and degree 0. The degree of the polynomial can be any non-zero integer i.e. can be 0 or greater than zero.

So the correct statement will be: 
An expression must have a monomial of degree 0 or higher to be a polynomial