How does the structure of a hummingbird's beak make it more successful in its environment?
a.
it allows gas exchange through the keratin of the beak while the bird is in flight.

b.
it allows hummingbirds to more easily attract mates by making a distinctive call.

c.
it allows the absorption of nutrients directly through the keratin of the beak.

d.
it allows hummingbirds to access certain nutrients more efficiently than other species.