First, ask yourself: What is a polynomial? It's an algebraic expression in which all powers of x are zero or positive integers.
Eliminate E because -2 is not a positive integer exponent.
Accept D because all of the powers of x are positive integers: {3, 2, 1, 0}
Eliminate C because -3 is not a positive integer power
Eliminate A and B because of the fractional or negative exponents shown.
Only D is a polynomial.
