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

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: Nobody really has such colorful eyes! The colors were added digitally after the photo was taken. They represent all the different colors of light. Light is a form of energy that travels in waves. Light of different colors has different wavelengths. Answer: wavelengths

A: Different colors of light differ in terms of which important attribute?
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Q: Passage: When the wind deposits sand, it forms small hills. These hills are called sand dunes ( Figure below ). For sand dunes to form, there must be plenty of sand and wind. Sand dunes are found mainly in deserts and on beaches. Answer: sand dunes

A:
When the wind deposits sand, it forms small hills, what are these hills called?
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