Given a scientific passage and an answer, generate a question for the given answer.

[EX Q]: Passage: Solar energy travels in photons. Photons travel in waves, which make up electromagnetic radiation. Answer: photons
[EX A]: Solar energy travels in what?

[EX Q]: Passage: Photography by Kat. Ferns are common in the understory of the tropical rainforest . CC BY 2.0. Answer: understory
[EX A]: In a tropical rainforest, where are ferns common?

[EX Q]: Passage: Examples of behaviors with annual cycles include migration and hibernation. Both are innate behaviors. They are triggered by changes in the environment, such as the days growing shorter in the fall. Answer: annual
[EX A]:
Triggered by changes in the environment, migration and hibernation occur as cycles on what temporal basis?