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 oxygen combines with hydrogen, which substance is formed?  
 (A) water (B) vinegar (C) hydrochloric acid (D) hydrogen dioxide
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: A lamp converts electrical energy to light energy. In addition to the light energy, much of this electrical energy is also converted to  
 (A) mechanical energy (B) chemical energy (C) heat energy (D) nuclear energy
Example Output:
C