instruction:
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.
question:
When animals use energy, they produce  
 (A) nitrogen (B) iron sulfide (C) oxygen (D) carbon dioxide
answer:
D


question:
Which of these is the center of our solar system?  
 (A) Mars (B) The moon (C) Jupiter (D) The sun
answer:
D


question:
Which best describes a proton?  
 (A) negatively charged and has a negligible mass (B) negatively charged and part of the nucleus (C) positively charged and part of the nucleus (D) negatively charged and orbits the nucleus
answer:

C