TASK DEFINITION: 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.
PROBLEM: When animals use energy, they produce  
 (A) nitrogen (B) iron sulfide (C) oxygen (D) carbon dioxide

SOLUTION: D

PROBLEM: Which of the following best describes an advantage of using a mass production manufacturing system instead of a custom manufacturing system?  
 (A) Customers can provide specific feedback to workers. (B) Workers become skilled in all aspects of assembly. (C) Goods can be easily modified for customers. (D) Products can be made at a lower cost.

SOLUTION: D

PROBLEM: The distance from Earth to the Sun is one astronomical unit. Which unit best describes how many astronomical units it is from Earth to the far end of the Milky Way Galaxy?  
 (A) hundreds (B) thousands (C) millions (D) billions

SOLUTION:
D