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.

Example Input: When animals use energy, they produce  
 (A) nitrogen (B) iron sulfide (C) oxygen (D) carbon dioxide
Example Output: D

Example Input: Which of these will best separate a saltwater solution?  
 (A) using a paper filtering system (B) using chromatography (C) allowing the salt to settle (D) allowing the water to evaporate
Example Output: D

Example Input: Why can a small fire be put out by placing a heavy blanket over it?  
 (A) This lowers the temperature. (B) This makes the flames smaller. (C) This absorbs the burning substance. (D) This keeps oxygen from reaching the fire.
Example Output:
D