Answer:
A, B, C and E are polynomial functions, D is not.
Step-by-step explanation:
An polynomial is an algebraic entity of the form:

Where
is the i-th coefficient and
is the order of the polynomial.
The function A is a third-order polynomial.
The function B is a second-order polynomial.
The function C is a third-order polynomial.
The function D is not a polynomial due to the presence of a square root.
The function E is a fourth-order polynomial.