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: Which two body systems are involved in inhaling oxygen and exhaling carbon dioxide?  
 (A) endocrine and skeletal (B) excretory and nervous (C) circulatory and respiratory (D) digestive and reproductive

Output: C


Input: Consider Input: Planting legumes in order to add nitrogen to soil most likely causes  
 (A) a decrease in the amount of acid rain. (B) an enrichment in the fertility of the soil. (C) an increase in the ratio of nitrogen to oxygen in the system. (D) a reduction in the soil's ability to manufacture its own nitrogen.


Output: B