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

[Q]: What is a close relationship between two species in which at least one species benefits called?
[A]: symbiosis

[Q]: What do we call the study of rock layers?
[A]: stratigraphy

[Q]: What is the nickname of the best-known geyser in the world, which erupts reliably every 90 minutes?
[A]:
old faithful