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: Prolonged exercise stimulates muscle cells to absorb sugar from the blood. This mechanism reduces stress placed on the body by signaling the body to produce  
 (A) insulin. (B) lipids. (C) hemoglobin. (D) hydrochloric acid.
Example Output: A

Example Input: The main function of a fish's fins is to help the fish  
 (A) reproduce (B) see (C) breathe (D) move
Example Output: D

Example Input: In what section of Earth do earthquakes happen?  
 (A) crust (B) mantle (C) inner core (D) outer core
Example Output:
A