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.

Example Input: The systems of the human body work together. Which system works with the skeletal system by pulling on the bones to create movement?  
 (A) digestive (B) circulatory (C) muscular (D) nervous
Example Output: C

Example Input: One type of animal hatches from an egg, breathes through gills when it is young, and mainly lives on land as an adult. Into which group is this animal classified?  
 (A) amphibians (B) birds (C) mammals (D) reptiles
Example Output: A

Example Input: Which of these statements about nonrenewable resources is true?  
 (A) They are inexpensive. (B) They help keep the air clean. (C) They can take millions of years to form. (D) They are used because they are easily removed from the ground.
Example Output:
C