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: Which force produces energy as heat?  
 (A) pull (B) gravity (C) friction (D) magnetic

Answer: C


Question: Which lists the diameter of the planets in order from smallest to largest?  
 (A) Venus, Earth, Mercury, Mars (B) Earth, Mars, Venus, Mercury (C) Mars, Mercury, Earth, Venus (D) Mercury, Mars, Venus, Earth

Answer: D


Question: Which is the best example of a pure substance?  
 (A) peanuts (B) milk (C) gold (D) air

Answer:
C