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.

[Q]: Proxima Centauri is the closest star to the Sun. Which units do astronomers most often use for the distance between Earth and Proxima Centauri?  
 (A) miles (B) meters (C) light years (D) astronomical units
[A]: C


[Q]: 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
[A]: D


[Q]: The elements sulfur (S) and oxygen combine to form a substance called sulfur dioxide (SO2). Sulfur dioxide is also formed when coal and oil are burned. Sulfur dioxide can best be described as  
 (A) a metal (B) an atom (C) a compound (D) a nonreactive gas
[A]:
C