Final answer:
A bird's sternum, known as a keel, is larger and more flexible compared to a human's sternum, as it is specialized to accommodate the powerful flight muscles needed for flying.
Step-by-step explanation:
How does a bird's sternum compare to yours? A bird's sternum, also known as keel or breastbone, is highly specialized for flight. Compared to a human's sternum, a bird's sternum is larger and has a bony ridge or keel that protrudes ventrally, to which powerful flight muscles are attached. Unlike humans, the sternum of birds is adapted to accommodate these large flight muscles necessary for the upstroke and downstroke motions during flight. Therefore, the correct answer would be (b) It is larger and more flexible, given the context of their function in flight.