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 the following is the best example of potential energy?  
 (A) a fallen rock (B) a burning match (C) a liter of gasoline (D) a red-hot piece of iron

Ex Output:
C


Ex Input:
The burning of fossil fuels affects the atmosphere by  
 (A) adding more heat and carbon dioxide. (B) reducing the amount of necessary heat. (C) taking water vapor out of the atmosphere. (D) putting more oxygen in the atmosphere.

Ex Output:
A


Ex Input:
Oxygen and iron combine chemically to form rust. Rust is classified as which of the following?  
 (A) an atom (B) a compound (C) an element (D) a mixture

Ex Output:

B