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: Why are some rocks smoother and rounder than others?  
 (A) They have the shapes of the minerals from which they are made. (B) They were smoothed by the action of wind and water. (C) They were squeezed up through the soil. (D) They hardened in rounded pockets of soil.
Example Output: B

Example Input: 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
Example Output: A

Example Input: The islands in the mid-Pacific Ocean region were formed by  
 (A) land subsidence. (B) deposition from currents. (C) wind and water erosion. (D) volcanic activity.
Example Output:
D