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:
Water vapor sometimes condenses into stratus clouds that are in contact with the ground. What forms as a result of this process?  
 (A) ozone (B) methane (C) fog (D) smoke

Ex Output:
C


Ex Input:
Which human organ system eliminates liquid and gaseous wastes from the body?  
 (A) circulatory (B) endocrine (C) excretory (D) reproductive

Ex Output:
C


Ex Input:
Which pair of systems is responsible for the flow of blood in the human body?  
 (A) circulatory and skeletal systems (B) skeletal and excretory systems (C) muscular and circulatory systems (D) respiratory and muscular systems

Ex Output:

C