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]: The systems of the human body work together. Which system works with the skeletal system by pulling on the bones to create movement?  
 (A) digestive (B) circulatory (C) muscular (D) nervous
[A]: C


[Q]: The molecule ATP is composed of elements commonly found in organic molecules. Which of the following is one of these elements?  
 (A) aluminum (B) calcium (C) phosphorus (D) tin
[A]: C


[Q]: A class wanted to see which paper airplane design could fly the farthest. In order to have the most accurate results, every student should  
 (A) use the same size of paper. (B) buy the same color of paper. (C) fold the paper the same way. (D) decorate the paper the same way.
[A]:
A