Explanation:
An interesting question to say the least. Nevertheless, you should know one basic thing about a polynomial. There are many rules, and I'd say to look up the rules with a simple search on purple math. Anyway,
Therefore I will go from left to right with what you have provided (then go to the bottom)
1st is NOT a polynomial
2nd IS a polynomial
3rd IS NOT a polynomial
4th IS NOT a polynomial
5th IS a polynomial
6th IS a polynomial