C. But see the answer under C. Apparently C is the accepted answer.
Explanation:
A. Not A.I don't think that's a problem for gulls especially on beaches.
B. Not B. Their feather do not look like they need much help in keeping their feathers attached when in flight.
C. This is not really the answer, but it is the best answer of these 4. The actual answer is that the bones are porous for better air intake which provides more oxygen and hence they are better able to fly.
D. Not D. Food has nothing to do with the problem. Birds get an adequate amount of food without their wings being porous. See the answer for C.
Since I have not seen the simulation, I can give a generic definition. A balanced chemical equation is when the mass of each element of the reactants (left side) is equal to the mass of each element in the products (right side).
