The Distribution of Weight in the Bird Skeleton Is

The distribution of weight in the bird skeleton is

A) top-heavy to improve flight.
B) heavier compared to a mammal of the same size,since a bird has to be lightweight to fly.
C) similar to or lighter in overall weight than a mammal,but heavier in the leg bones,which lowers the bird's center of gravity.
D) loaded into a heavier bird skull,since the high speed requires a "safety helmet."
E) roughly the same as a mammal of the same size.