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

[EX Q]: Passage: Earth's climate has changed many times. Long warm periods were broken up by ice ages. Over the past 150 years, climate has warmed quickly. Answer: ice ages
[EX A]: What occurs between long warm climate periods?

[EX Q]: Passage: Experiments are sometimes hard or even impossible to do. For example, a scientist who is studying an extinct animal cannot experiment with the animal because it no longer exists. The scientist must rely instead on evidence in the natural world, such as fossils that the extinct animal left behind. Answer: experiments
[EX A]: What can be hard or even impossible to perform in a scientific sense?

[EX Q]: Passage: The major types of radioactivity include alpha particles, beta particles, and gamma rays. Answer: radioactivity
[EX A]:
Alpha particles, beta particles, and gamma particles are major types of what?