Given a scientific question, generate a correct answer to it.

Ex Input:
The fossilized skeleton of archaeopteryx looks like that of a dinosaur, but it had what structures modified for flight, a trait associated only with birds among modern animals?

Ex Output:
feathers

Ex Input:
What keeps the moon orbiting earth?

Ex Output:
gravity

Ex Input:
What is root that does not arise from a usual place?

Ex Output:
adventitious