TASK DEFINITION: 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.
PROBLEM: 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.

SOLUTION: A

PROBLEM: Which of these warms most of the air, water, and land on Earth?  
 (A) Coal (B) Electricity (C) Sunlight (D) Wind

SOLUTION: C

PROBLEM: A student determined the density of different bars of soap. Which should the student most likely do to check the accuracy of the results?  
 (A) complete the experiment in one day (B) test multiple brands of soap (C) record data in metric units (D) repeat the experiment

SOLUTION:
D