You are given a science question (easy-level) and four answer options (associated with "A", "B", "C", "D"). Your task is to find the correct answer based on scientific facts, knowledge, and reasoning. Do not generate anything else apart from one of the following characters: 'A', 'B, 'C', 'D'. There is only one correct answer for each question.

Q: Which of the following best describes a mineral?  
 (A) a solid natural material with a crystal structure (B) a material that was once living but has decayed (C) a liquid chemical used to make soil more fertile (D) a nutrient produced by plants that other organisms need

A: A
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Q: In some locations, squirrels sleep for long periods of time during the winter months. Which of the following most likely causes these squirrels to sleep for long periods of time?  
 (A) increase in humidity (B) decrease in temperature (C) clouds forming in the sky (D) winds blowing in the night

A: B
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Q: A sunspot appears as a dark spot on the sun that is cooler than the surrounding area. On which region of the sun do sunspots occur?  
 (A) chromosphere (B) core (C) corona (D) photosphere

A:
D
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