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

Q: Passage: Like a blanket on a sleeping person, greenhouse gases act as insulation for the planet. The warming of the atmosphere is because of insulation by greenhouse gases. Greenhouse gases are the component of the atmosphere that moderate Earth's temperatures. Answer: insulation

A: Like a blanket on a sleeping person, greenhouse gases act as what for the planet?
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Q: Passage: What does sunshine have to do with sleep (other than the sun shining in your eyes and waking you up)? For many people, sleeping problems have to do with an amine that the brain makes called melatonin. This compound affects the sleep-wake cycle and is affected by sunlight. During the winter, the daily cycle of melatonin production may be affected by less sunlight hours. If this cycle is changed, the person may have trouble sleeping. Melatonin supplements are available in pharmacies and health food stores and may be of help for those with sleeping problems. Answer: melatonin

A: During the winter, production of what amine involved in the sleep-wake cycle may be affected by less sunlight hours?
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Q: Passage: Again, the transfer of an H + ion leaves the oxidation numbers unaffected. In summary, redox reactions can always be recognized by a change in oxidation number of two of the atoms in the reaction. Any reaction in which no oxidation numbers change is not a redox reaction. Answer: oxidation

A:
Redox reactions can always be recognized by a change in what number of two of the atoms in the reaction?
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