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

Q: Passage: New mitochondria and chloroplasts are produced through a process similar to binary fission . Bacteria also reproduce through binary fission. Answer: binary fission

A: How do bacteria reproduce?
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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

A: What occurs between long warm climate periods?
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Q: Passage: Sublimation occurs when ice and snow change directly to water vapor. This also happens because of heat from the sun. Answer: when the ice and snow change directly into water vapors

A:
When does sublimation occur?
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