Which Statement Best Sums Up Our Understanding of How Animals

Which statement best sums up our understanding of how animals navigate during migration?

A) The mechanisms have been worked out in great detail, from the genes involved, to the brain structures, to the resulting behavior.
B) We have a thorough understanding of orientation but not navigation.
C) We have some understanding of the information different animals rely on (sun, stars, or magnetic fields) , and some sensory structures, but beyond that the mechanisms are still mysterious.
D) Animal navigation is a complete mystery.