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.

Input: Consider 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.

Output: B


Input: Consider Input: When animals use energy, they produce  
 (A) nitrogen (B) iron sulfide (C) oxygen (D) carbon dioxide

Output: D


Input: Consider Input: The process of digestion breaks down proteins into smaller molecules that are used to rebuild other proteins. During digestion, proteins undergo  
 (A) cell division. (B) nuclear reactions. (C) natural selection. (D) chemical changes.


Output: D