Descending order means in decreasing order.
So for the polynomial we have to check the exponents. If the exponents are in decreasing order, we say that the polynomial is in descending order.
From the given options only option C lists the polynomial in descending order starting with exponent 7 then 5, 4, 3 and constant term. Rest of the options do not list the polynomial in descending order.
So the answer to this question is Option C