TASK DEFINITION: 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.
PROBLEM: The fusion reaction that fuels the Sun converts hydrogen into  
 (A) carbon. (B) iron. (C) neon. (D) helium.

SOLUTION: D

PROBLEM: 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.

SOLUTION: C

PROBLEM: Which of the following statements best describes photosynthesis?  
 (A) Carbon dioxide and water are turned into sugar and oxygen. (B) Sugar and oxygen are turned into water and carbon dioxide. (C) Oxygen and carbon dioxide are turned into water and sugar. (D) Water and sugar are turned into oxygen and carbon dioxide.

SOLUTION:
A