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: As the molecules of water begin to slow down they go into a phase where they are no longer able to easily move past each other. The water is passing through a phase change and will     
 (A) remain a mixture. (B) remain a compound. (C) become an element. (D) become a compound.
Example Output: B

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: The Moon and Earth have a similar  
 (A) surface atmosphere. (B) rocky terrain. (C) gravity. (D) size.
Example Output:
B