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

Q: Passage: The cardiovascular system moves nutrients and other substances throughout the body. Answer: cardiovascular system

A: Which human body system system moves nutrients and other substances throughout the body?
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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: Oxygen is needed to make ozone. Ozone is a molecule made of three oxygen ions. Ozone in the upper atmosphere blocks harmful solar radiation from reaching the surface. Without oxygen, life on Earth would have been very simple. Answer: three

A:
How many oxygen ions make up an ozone molecule?
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