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: What form of energy is being used when a person pushes a wooden block across the floor?  
 (A) mechanical (B) magnetic (C) sound (D) electrical
Example Output: A

Example Input: Many scientists are convinced that an increase of certain gases in the atmosphere is affecting global temperatures. What makes this hypothesis difficult to prove?  
 (A) Trees absorb these gases. (B) Global temperatures are rising. (C) Many variables affect global temperatures. (D) Many human activities produce these gases.
Example Output: C

Example Input: The Milky Way Galaxy is visible as a bright region in the night sky. Modern telescopic observation has made it possible to discover that the brightness of the Milky Way Galaxy is due primarily to which structure?  
 (A) clouds of hot gas (B) large numbers of stars (C) high energy compounds (D) extremely reflective ice particles
Example Output:
B