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: Which characteristic best identifies a pure substance?  
 (A) shape (B) texture (C) melting point (D) state of matter

Output: C


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

Output: D


Input: Consider Input: Two parent butterflies with normal wings have offspring with altered wing shapes. What most likely caused this change?  
 (A) speciation (B) an adaptation (C) natural selection (D) a genetic mutation


Output: D