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: Proxima Centauri is the closest star to the Sun. Which units do astronomers most often use for the distance between Earth and Proxima Centauri?  
 (A) miles (B) meters (C) light years (D) astronomical units

Output: C


Input: Consider Input: Humans are protected from some infections by specialized cells which produce chemicals that  
 (A) destroy microbes (B) recycle nutrients (C) allow locomotion (D) coordinate movement


Output: A