You are given a science question (hard-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: Dr. Tanaka discovered a new virus. The virus has a single strand of a nucleic acid, but she does not know if it is DNA or RNA. After running tests, she concludes that it is DNA. Which of the following would lead her to that conclusion?  
 (A) It contains uracil. (B) It contains adenine. (C) It contains thymine. (D) It contains cytosine.
Example Output: C

Example Input: Which of these is an environmental benefit of converting to solar energy?  
 (A) a decrease in air pollution (B) an increase in the cost of energy (C) an increase in the use of fossil fuels (D) a decrease in electrical energy production
Example Output: A

Example Input: Which BEST describes the surface of the Earth over billions of years?  
 (A) A flat surface is gradually pushed up into higher and higher mountains until the Earth is covered with mountains. (B) High mountains gradually wear down until most of the Earth is at sea level. (C) High mountains gradually wear down as new mountains are continuously being formed, over and over again. (D) High mountains and flat plains stay side by side for billions of years with little change.
Example Output:
C