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 these are scientific classifications for galaxies in the universe?  
 (A) dust, gas, ice (B) small, medium, large (C) spiral, elliptical, irregular (D) red giant, white dwarf, supernova

A: C
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Q: Which of these cycles takes 24 hours?  
 (A) Earth rotating on its axis (B) Earth revolving around the Sun (C) the Moon rotating on its axis (D) the Moon revolving around Earth

A: A
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Q: Which human organ system produces most of the hormones that regulate body functions?  
 (A) digestive (B) nervous (C) muscular (D) endocrine

A:
D
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