Which of the following adaptations helps birds fly? They have more fat than most animals, so they can fly for long distances.
They have more fat than most animals, so they can fly for long distances.

They have hollow bones, so they are lighter.
They have hollow bones, so they are lighter.

They have smaller blood vessels, so their hearts have to work less in flight.
They have smaller blood vessels, so their hearts have to work less in flight.

They have a larger stomach, so they can absorb food faster.
They have a larger stomach, so they can absorb food faster.