To answer this question, we need to take into account that:
1. A polynomial is a finite sum of terms.
2. All the variables have a whole number as an exponent.
3. None of the variables appear in a denominator.
Having this information, we can say that:
First case:
We can see that this IS NOT a polynomial, in the sense that the term -4^(2x) is an exponential function.
Second Case:
For this case, we see that in the second term, the variable appears in the denominator. Therefore, this is NOT a polynomial function.
Third Case:
This case is similar to the previous one. Then, this is NOT a polynomial function.
Fourth Case:
In this case, we can see that the exponents in the variables are whole numbers (2 and 1). None of the variables appear in the denominator, and it is a finite number of terms. Therefore, this IS a polynomial function (even if it has radical 3).
Hence, the only function that is a polynomial is option D.