The longer the migratory route, the more fat migrating birds must accumulate as fuel for their flight. The gain in body mass would make birds obese by human standards, and should render them unable to fly, but this gain is (i)____________ premigratory (ii)____________ of digestive organs, inactive during migration, and by the (iii)____________ of the muscles that power the flight. A. partially offset by B. shrinking C. strengthening D. strongly suggestive of E. specialization F. attenuation G. seemingly unrelated to H. capacity I. responsiveness