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.

Ex 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.

Ex Output:
C


Ex Input:
Which difference between water and ice results in ice floating on cold water?  
 (A) heat (B) shape (C) density (D) volume

Ex Output:
C


Ex Input:
People take in and release gases from the air when they breathe. Which exhaled gas is a waste product of respiration?  
 (A) oxygen (B) helium (C) hydrogen (D) carbon dioxide

Ex Output:

D