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.

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
C

Which organisms contribute most to the decomposition of dead organisms?  
 (A) snakes (B) viruses (C) insects (D) bacteria
D

Which is a primary energy source used by power plants to generate electricity?  
 (A) coal (B) wood (C) gasoline (D) batteries

A