Ways to spot if an expression is not a polynomial:
1) If there is a negative exponent
2) If there is division by a variable
3) If the power is something other than a non-negative integer
If any of these conditions exist, the expression will not be a polynomial. Now consider the options. Option A has negative exponent, Option B involves division by a variable and Option D has a exponent which is not a number.
So, from the given options, option C is the only polynomial
