Identify the variable expression that is not a polynomial: . a: x+12. b: 33. c: x^9+y^3. d: y^9+27

The term polynomial comes from the words poly- which means "many" and -nomial meaning "terms". In mathematics, a polynomial is an expression that consists of variables and coefficients wherein it only utilizes addition, subtraction, multiplication and a non-negative integer. In the given options above, the variable expression that is not a polynomial is option C. x^9+y^3.