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 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: Some birds fly south in the fall and return in the spring. This is an example of  
 (A) migration (B) camouflage (C) hibernation (D) growth

Output: A


Input: Consider Input: When igneous rock is changed into metamorphic rock, which form of energy is this process?  
 (A) heat (B) chemical (C) magnetic (D) light


Output: A