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.

[EX Q]: What happens at the boiling point of a substance?  
 (A) liquid becomes a gas (B) solid becomes a gas (C) liquid becomes a solid (D) solid becomes a liquid
[EX A]: A

[EX Q]: Which of these is the center of our solar system?  
 (A) Mars (B) The moon (C) Jupiter (D) The sun
[EX A]: D

[EX Q]: A student must explain the role of dead leaves in the ecosystem. Which statement will the student most likely provide to explain the importance of these leaves?  
 (A) The leaves provide shelter to growing seeds. (B) The decay of the leaves provides nutrients to other plants. (C) The leaves release chlorophyll into the grass as they decay. (D) The leaves prevent fungus from growing at the base of the tree.
[EX A]:
B