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 body systems are most involved in the response when someone stubs his or her toe?  
 (A) nervous and muscle (B) muscle and endocrine (C) nervous and digestive (D) reproductive and circulatory

A: A
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Q: Which organ is the site of gas exchange between the body and the environment?  
 (A) spleen (B) liver (C) lungs (D) pancreas

A: C
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Q: A cyclist travels 3 km north in 25 minutes. What does this information describe?  
 (A) mass (B) force (C) motion (D) gravity

A:
C
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