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: Water freezing is an example of a  
 (A) liquid changing to a solid (B) solid changing to a liquid (C) gas changing to a solid (D) gas changing to a liquid
Example Output: A

Example Input: Which organ in a frog has a function similar to the function of lungs in a bird?  
 (A) kidney (B) skin (C) liver (D) heart
Example Output: B

Example Input: High-pressure systems stop air from rising into the colder regions of the atmosphere where water can condense. What will most likely result if a high-pressure system remains in an area for a long period of time?  
 (A) fog (B) rain (C) drought (D) tornado
Example Output:
C