Given the fact "migration is an instinctive behavior", what is the answer to the question or completion "An example of an instinctive behavior is"

Select from the following.
[A]. a herd of zebras heading in the direction of rain clouds at the end of the dry season.
[B]. a baby bird falling from its nest.
[C]. a horse following the commands of its rider.
[D]. a bird dying from an infection.
[A].