instruction:
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.
question:
When animals use energy, they produce  
 (A) nitrogen (B) iron sulfide (C) oxygen (D) carbon dioxide
answer:
D


question:
Which object is best used to demonstrate the bending of light as it passes through a substance?  
 (A) convex lens (B) flat mirror (C) opaque rod (D) concave mirror
answer:
A


question:
Penny's class was learning how rapidly some changes can happen on Earth. Which event causes the fastest change to the surface of Earth?  
 (A) water flowing in a riverbed (B) a wave crashing on a beach (C) an earthquake cracking a road (D) wind blowing against a mountain
answer:

C