Answer:
All of them are polynomials except c.
Explanation:
Polynomials are in the form:

You can see here there are no extra symbols like square root, cube root, absolute value, and so on on the variable x...
We also don't have division by a variable. All the exponents are whole numbers.
a) While it has a square root, it is not on a variable so a is a polynomial. The exponents on the variables are whole numbers.
b) b is a polynomial also because all the exponents are whole numbers.
c) This is not a polynomial because there is a square root on a variable.
d) This is a polynomial. All the exponents are whole numbers.