polynomial: is a mathematical expression of one or more algebraic terms each of which consists of a constant multiplied by one or more variables raised to a non-negative integral power
With this definition we can eliminate the first one and second one.
The third one cannot be right because it does not have a constant being multiplied by a variable and so on.
I think it is the last one since it is the only one that has a constant multiplied by a variable raised to an integral power.
D is correct.
