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: Humans use both renewable and nonrenewable resources. Which human activity uses a nonrenewable resource?  
 (A) building houses with wood (B) using natural gas to heat homes (C) using solar energy to power lights (D) producing electricity from flowing water

A: B
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Q: One substance found on Earth is more stable as an elemental gas than as part of a solid compound. As a result, this substance is very abundant in the atmosphere. Which substance exhibits these traits?  
 (A) argon (B) chlorine (C) nitrogen (D) oxygen

A: C
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Q: Toni got a cut on her arm while playing in a softball game. A few weeks later, the cut was healed. Which process is most responsible for repairing the cut?  
 (A) signals transported by nerve cells (B) exchange of oxygen in the lungs (C) transport of waste by blood (D) reproduction of skin cells

A:
D
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